[Playlist] Guard Open in Finder against empty set

Guard Open in Finder against being called on a playlist with no
selection, which may happen if the action is triggered on an empty
playlist, which would cause an array out of bounds access error.

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

Playlist/PlaylistController.m

@@ -1282,6 +1282,8 @@ static inline void dispatch_sync_reentrant(dispatch_queue_t queue, dispatch_bloc
 }
 
 - (IBAction)showEntryInFinder:(id)sender {
+	if([[self selectedObjects] count] == 0) return;
+
 	NSWorkspace *ws = [NSWorkspace sharedWorkspace];
 
 	NSURL *url = [[self selectedObjects][0] URL];