How to stop the Unity FirstPersonController from jumping twice?

The FirstPersonController from Unity's Standard Assets. If you press space while in the air, when you hit the ground, you will immediately jump again. Can somebody help me fix this? Here is FirstPersonController.cs

 using System;
 using UnityEngine;
 using UnityStandardAssets.CrossPlatformInput;
 using UnityStandardAssets.Utility;
 using Random = UnityEngine.Random;
 
 #pragma warning disable 618, 649
 namespace UnityStandardAssets.Characters.FirstPerson
 {
     [RequireComponent(typeof (CharacterController))]
     [RequireComponent(typeof (AudioSource))]
     public class FirstPersonController : MonoBehaviour
     {
         [SerializeField] public bool m_IsWalking;
         [SerializeField] public float m_WalkSpeed;
         [SerializeField] public float m_RunSpeed;
         [SerializeField] [Range(0f, 1f)] public float m_RunstepLenghten;
         [SerializeField] public float m_JumpSpeed;
         [SerializeField] public float m_StickToGroundForce;
         [SerializeField] public float m_GravityMultiplier;
         [SerializeField] public MouseLook m_MouseLook;
         [SerializeField] public bool m_UseFovKick;
         [SerializeField] public FOVKick m_FovKick = new FOVKick();
         [SerializeField] public bool m_UseHeadBob;
         [SerializeField] public CurveControlledBob m_HeadBob = new CurveControlledBob();
         [SerializeField] public LerpControlledBob m_JumpBob = new LerpControlledBob();
         [SerializeField] public float m_StepInterval;
         [SerializeField] private AudioClip[] m_FootstepSounds;    // an array of footstep sounds that will be randomly selected from.
         [SerializeField] private AudioClip m_JumpSound;           // the sound played when character leaves the ground.
         [SerializeField] private AudioClip m_LandSound;           // the sound played when character touches back on ground.
 
         private Camera m_Camera;
         private bool m_Jump;
         private float m_YRotation;
         private Vector2 m_Input;
         private Vector3 m_MoveDir = Vector3.zero;
         private CharacterController m_CharacterController;
         private CollisionFlags m_CollisionFlags;
         private bool m_PreviouslyGrounded;
         private Vector3 m_OriginalCameraPosition;
         private float m_StepCycle;
         private float m_NextStep;
         private bool m_Jumping;
         private AudioSource m_AudioSource;
 
         // Use this for initialization
         private void Start()
         {
             m_CharacterController = GetComponent<CharacterController>();
             m_Camera = Camera.main;
             m_OriginalCameraPosition = m_Camera.transform.localPosition;
             m_FovKick.Setup(m_Camera);
             m_HeadBob.Setup(m_Camera, m_StepInterval);
             m_StepCycle = 0f;
             m_NextStep = m_StepCycle/2f;
             m_Jumping = false;
             m_AudioSource = GetComponent<AudioSource>();
             m_MouseLook.Init(transform , m_Camera.transform);
         }
 
 
         // Update is called once per frame
         private void Update()
         {
             RotateView();
             // the jump state needs to read here to make sure it is not missed
             if (!m_Jump)
             {
                 m_Jump = CrossPlatformInputManager.GetButtonDown("Jump");
             }
 
             if (!m_PreviouslyGrounded && m_CharacterController.isGrounded)
             {
                 StartCoroutine(m_JumpBob.DoBobCycle());
                 PlayLandingSound();
                 m_MoveDir.y = 0f;
                 m_Jumping = false;
             }
             if (!m_CharacterController.isGrounded && !m_Jumping && m_PreviouslyGrounded)
             {
                 m_MoveDir.y = 0f;
             }
 
             m_PreviouslyGrounded = m_CharacterController.isGrounded;
         }
 
 
         private void PlayLandingSound()
         {
             m_AudioSource.clip = m_LandSound;
             m_AudioSource.Play();
             m_NextStep = m_StepCycle + .5f;
         }
 
 
         private void FixedUpdate()
         {
             float speed;
             GetInput(out speed);
             // always move along the camera forward as it is the direction that it being aimed at
             Vector3 desiredMove = transform.forward*m_Input.y + transform.right*m_Input.x;
 
             // get a normal for the surface that is being touched to move along it
             RaycastHit hitInfo;
             Physics.SphereCast(transform.position, m_CharacterController.radius, Vector3.down, out hitInfo,
                                m_CharacterController.height/2f, Physics.AllLayers, QueryTriggerInteraction.Ignore);
             desiredMove = Vector3.ProjectOnPlane(desiredMove, hitInfo.normal).normalized;
 
             m_MoveDir.x = desiredMove.x*speed;
             m_MoveDir.z = desiredMove.z*speed;
 
 
             if (m_CharacterController.isGrounded)
             {
                 m_MoveDir.y = -m_StickToGroundForce;
 
                 if (m_Jump)
                 {
                     m_MoveDir.y = m_JumpSpeed;
                     PlayJumpSound();
                     m_Jump = false;
                     m_Jumping = true;
                 }
             }
             else
             {
                 m_MoveDir += Physics.gravity*m_GravityMultiplier*Time.fixedDeltaTime;
             }
             m_CollisionFlags = m_CharacterController.Move(m_MoveDir*Time.fixedDeltaTime);
 
             ProgressStepCycle(speed);
             UpdateCameraPosition(speed);
 
             m_MouseLook.UpdateCursorLock();
         }
 
 
         private void PlayJumpSound()
         {
             m_AudioSource.clip = m_JumpSound;
             m_AudioSource.Play();
         }
 
 
         private void ProgressStepCycle(float speed)
         {
             if (m_CharacterController.velocity.sqrMagnitude > 0 && (m_Input.x != 0 || m_Input.y != 0))
             {
                 m_StepCycle += (m_CharacterController.velocity.magnitude + (speed*(m_IsWalking ? 1f : m_RunstepLenghten)))*
                              Time.fixedDeltaTime;
             }
 
             if (!(m_StepCycle > m_NextStep))
             {
                 return;
             }
 
             m_NextStep = m_StepCycle + m_StepInterval;
 
             PlayFootStepAudio();
         }
 
 
         private void PlayFootStepAudio()
         {
             if (!m_CharacterController.isGrounded)
             {
                 return;
             }
             // pick & play a random footstep sound from the array,
             // excluding sound at index 0
             int n = Random.Range(1, m_FootstepSounds.Length);
             m_AudioSource.clip = m_FootstepSounds[n];
             m_AudioSource.PlayOneShot(m_AudioSource.clip);
             // move picked sound to index 0 so it's not picked next time
             m_FootstepSounds[n] = m_FootstepSounds[0];
             m_FootstepSounds[0] = m_AudioSource.clip;
         }
 
 
         private void UpdateCameraPosition(float speed)
         {
             Vector3 newCameraPosition;
             if (!m_UseHeadBob)
             {
                 return;
             }
             if (m_CharacterController.velocity.magnitude > 0 && m_CharacterController.isGrounded)
             {
                 m_Camera.transform.localPosition =
                     m_HeadBob.DoHeadBob(m_CharacterController.velocity.magnitude +
                                       (speed*(m_IsWalking ? 1f : m_RunstepLenghten)));
                 newCameraPosition = m_Camera.transform.localPosition;
                 newCameraPosition.y = m_Camera.transform.localPosition.y - m_JumpBob.Offset();
             }
             else
             {
                 newCameraPosition = m_Camera.transform.localPosition;
                 newCameraPosition.y = m_OriginalCameraPosition.y - m_JumpBob.Offset();
             }
             m_Camera.transform.localPosition = newCameraPosition;
         }
 
 
         private void GetInput(out float speed)
         {
             // Read input
             float horizontal = CrossPlatformInputManager.GetAxis("Horizontal");
             float vertical = CrossPlatformInputManager.GetAxis("Vertical");
 
             bool waswalking = m_IsWalking;
 
 #if !MOBILE_INPUT
             // On standalone builds, walk/run speed is modified by a key press.
             // keep track of whether or not the character is walking or running
             m_IsWalking = !Input.GetKey(KeyCode.LeftShift);
 #endif
             // set the desired speed to be walking or running
             speed = m_IsWalking ? m_WalkSpeed : m_RunSpeed;
             m_Input = new Vector2(horizontal, vertical);
 
             // normalize input if it exceeds 1 in combined length:
             if (m_Input.sqrMagnitude > 1)
             {
                 m_Input.Normalize();
             }
 
             // handle speed change to give an fov kick
             // only if the player is going to a run, is running and the fovkick is to be used
             if (m_IsWalking != waswalking && m_UseFovKick && m_CharacterController.velocity.sqrMagnitude > 0)
             {
                 StopAllCoroutines();
                 StartCoroutine(!m_IsWalking ? m_FovKick.FOVKickUp() : m_FovKick.FOVKickDown());
             }
         }
 
 
         private void RotateView()
         {
             m_MouseLook.LookRotation (transform, m_Camera.transform);
         }
 
 
         private void OnControllerColliderHit(ControllerColliderHit hit)
         {
             Rigidbody body = hit.collider.attachedRigidbody;
             //dont move the rigidbody if the character is on top of it
             if (m_CollisionFlags == CollisionFlags.Below)
             {
                 return;
             }
 
             if (body == null || body.isKinematic)
             {
                 return;
             }
             body.AddForceAtPosition(m_CharacterController.velocity*0.1f, hit.point, ForceMode.Impulse);
         }
     }
 }