Set preview song as selected song if entering the highscore of that song

This should make sure, that the song is still selected and will be previewed without interruption after closing the high score.

Vocaluxe/Screens/CScreenSong.cs

@@ -1000,6 +1000,7 @@ namespace Vocaluxe.Screens
         {
             CGame.ClearSongs();
             CScreenSong.setStaticSelectedSongID(CSongs.VisibleSongs[_SongMenu.GetPreviewSongNr()].ID);
+            _SongMenu.SetSelectedSong(_SongMenu.GetPreviewSongNr());
             CBase.Graphics.FadeTo(EScreen.Highscore);
         }