Merge pull request #347 from lukeIam/release-0.4.1

_PreviewStartHelperTask null check from @Pr3di

Vocaluxe/Base/CBackgroundMusic.cs

@@ -323,7 +323,7 @@ namespace Vocaluxe.Base
             
 
             //Change song position only if song is changed or near to end
-            if (songChanged || _CurPlayer.Position + 30 < _CurPlayer.Length)
+            if (songChanged || _CurPlayer.Position + 30 < _CurPlayer.Length || _PreviewStartHelperTask == null)
             {
                 lock (_PreviewStartHelperTaskLock)
                 {