[Playlist] Guard entry selection against empty set

Guard the playlist entry retrieval function against being called on an
empty playlist, because an empty playlist would result in a division by
zero error to occur here.

Signed-off-by: Christopher Snowhill <kode54@gmail.com>

Playlist/PlaylistController.m

@@ -885,6 +885,8 @@ static inline void dispatch_sync_reentrant(dispatch_queue_t queue, dispatch_bloc
 }
 
 - (PlaylistEntry *)entryAtIndex:(NSInteger)i {
+	if([[self arrangedObjects] count] == 0) return nil;
+
 	RepeatMode repeat = [self repeat];
 
 	if(i < 0 || i >= [[self arrangedObjects] count]) {