returned to threaded cover loading: there are no threading problems and its a lot faster!

Vocaluxe/Base/CGraphics.cs

@@ -311,7 +311,7 @@ namespace Vocaluxe.Base
             CInput.Update();
 
             if (CConfig.CoverLoading == ECoverLoading.TR_CONFIG_COVERLOADING_DYNAMIC && _CurrentScreen != EScreens.ScreenSing)
-                CSongs.LoadCover(30, 1);
+                CSongs.LoadCover();
 
             if (CSettings.GameState != EGameState.EditTheme)
             {