Correct null pointer

src/main/java/net/Broken/audio/TrackScheduler.java

@@ -153,6 +153,7 @@ public class TrackScheduler extends AudioEventAdapter {
         // Start the next track, regardless of if something is already playing or not. In case queue was empty, we are
         // giving null to startTrack, which is a valid argument and will simply stop the player.
         UserAudioTrack track = queue.poll();
+        if(track != null)
             this.currentPlayingTrack = track;
         if(track != null)
             player.startTrack(track.getAudioTrack(), false);