Next song problem (music player)

Hi guys, i did this music player, the problem is that if i put for example ten song number, and drag them in song list, when i arrived at the last song (10 for this case) and click on the next song, the script read more than ten songs (it reads infinite songs) How can i set the song limit at 10? I wrote var SongNumber : int = 10; but don't work :/

 var CurrentSong : AudioClip = null;
 var SongList : AudioClip[];
 var gSkin : GUISkin;
 var SongName : String;
 var Music : AudioSource;
 //per usare lo stex input!
 var on : boolean; 
  
  
 var SongNumber : int = 10;
 
 var showGUI : boolean = false;
 
 
 //Volume Audio 
  var hSliderValue : float = 0.0;
  
  
 function Start(){
 
     
     CurrentSong = SongList[SongNumber];
     Music = gameObject.GetComponent(AudioSource);
     Music.loop = false;
     Music.playOnAwake = false;
     Music.clip = CurrentSong;
     Music.volume = 2;
  
 audio.Play();
  
 NextSong();
 
 }
 
 function Update () {
 
 
 //Volume Audio 
 audio.volume = hSliderValue; 
  
 SongName = CurrentSong.name;
  
 Music = gameObject.GetComponent(AudioSource);
 Music.clip = CurrentSong;
  
 
 
 if (SongNumber > SongList.length - 1)
 {
     SongNumber = 0;
 }
 if (SongNumber < 0)
 {
     SongNumber = SongList.length - 1;
 }
 
 }
 
 
 
 
 
 function OnMouseDown () {
     if (Input.GetMouseButton){
     
     //Per usare lo stex Input!
     on= !on;
     
     if (!on) {
     showGUI = true;
     }
     if (on) {
     showGUI = false;
        
 }
 }
 }
 
 
 
  
 function OnGUI(){
 
 if(showGUI){
 
 
 
 GUI.skin = gSkin;
  
 GUI.Box(Rect(10, Screen.height-125, 420, 130), SongName);
 
 
 //Volume Audio
 hSliderValue = GUI.HorizontalSlider (Rect (180, Screen.height-28, 180, 100), hSliderValue, 0.0, 1.0);
 
  
 if(GUI.Button(Rect(30, Screen.height-41, 40, 40), "<<")){
     SongNumber -= 1;
     CurrentSong = SongList[SongNumber];
     Wait();
 }
  
 if(audio.isPlaying){
     if(GUI.Button(Rect(75, Screen.height-41, 40, 40), "||")){
        audio.Pause();
     }
 }
  
 if(!audio.isPlaying){
     if(GUI.Button(Rect(75, Screen.height-41, 40, 40), ">")){
        audio.Play();
     }
 }
  
 if(GUI.Button(Rect(120, Screen.height-41, 40, 40), ">>")){
     SongNumber += 1;
     CurrentSong = SongList[SongNumber];
     Wait();
 }
  
 }
 }
  
 function Wait(){
 yield WaitForSeconds(0.05);
 audio.Play();
  
 }
  
 function NextSong(){
 yield WaitForSeconds (audio.clip.length);
     SongNumber += 1;
     CurrentSong = SongList[SongNumber];
     Wait();
 }