Merge remote-tracking branch 'upstream/develop' into medley

Vocaluxe/Screens/CScreenSong.cs

@@ -384,7 +384,7 @@ namespace Vocaluxe.Screens
                 int SongNr = IDs[CGame.Rand.Next(IDs.Count)];
 
                 EGameMode gm = EGameMode.TR_GAMEMODE_NORMAL;
-                if (CSongs.VisibleSongs[SongNr].IsDuet)
+                if (CSongs.AllSongs[SongNr].IsDuet)
                     gm = EGameMode.TR_GAMEMODE_DUET;
                 CGame.AddSong(SongNr, gm);