some fixes.

VocaluxeLib/Menu/SongMenu/CSongMenuTileBoard.cs

@@ -111,7 +111,7 @@ namespace VocaluxeLib.Menu.SongMenu
             {
                 if (value == base._PreviewNr)
                 {
-                    if (!CBase.BackgroundMusic.IsPlaying())
+                    if (!CBase.BackgroundMusic.IsPlaying() && value != -1)
                         CBase.BackgroundMusic.PlayPreview();
                     return;
                 }

VocaluxeLib/Utils/Player/CSoundPlayer.cs

@@ -84,7 +84,7 @@ namespace VocaluxeLib.Utils.Player
 
         public void Play()
         {
-            if (_StreamID == -1)
+            if (_StreamID == -1 || IsPlaying)
                 return;
 
             CBase.Sound.SetPosition(_StreamID, _StartPosition);