Fix crash when Quitting without active track set.

Application/PlaybackEventController.m

@@ -108,6 +108,8 @@ didReceiveNotificationResponse:(UNNotificationResponse *)response
 - (NSDictionary *)fillNotificationDictionary:(PlaylistEntry *)pe status:(TrackStatus)status
 {
     NSMutableDictionary *dict = [NSMutableDictionary dictionary];
+    if (pe == nil)
+        return dict;
     
     [dict setObject:[[pe URL] absoluteString] forKey:TrackPath];
     if ([pe title]) [dict setObject:[pe title] forKey:TrackTitle];