MusicHandler: properly skip tracks on error.

src/main/java/moe/nekojimi/chords/MusicHandler.java

@@ -105,7 +105,8 @@ public class MusicHandler implements AudioSendHandler, Closeable, Consumer<Track
         } catch (UnsupportedAudioFileException | IOException ex)
         {
             Logger.getLogger(Chords.class.getName()).log(Level.SEVERE, null, ex);
-            skipTrack();
+            currentTrack = null;
+            requestTrack();
         } finally
         {
         }