NPE in HlsMediaSource.releaseSource()

[komissarovdenis]

Sometimes I have a crash with this stacktrace.
Probably it happens when non prepared Source is goes to be released.
Could you, please, add check playlistTracker for null when releaseSource() is called?
Lib version is 2.1.1

AndroidRuntime: FATAL EXCEPTION: ExoPlayerImplInternal:Handler
    Process: com.xxx, PID: 5770
    java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.exoplayer2.source.hls.playlist.HlsPlaylistTracker.release()' on a null object reference
                 at com.google.android.exoplayer2.source.hls.HlsMediaSource.releaseSource(HlsMediaSource.java:97)
                 at com.google.android.exoplayer2.ExoPlayerImplInternal.resetInternal(ExoPlayerImplInternal.java:698)
                 at com.google.android.exoplayer2.ExoPlayerImplInternal.stopInternal(ExoPlayerImplInternal.java:658)
                 at com.google.android.exoplayer2.ExoPlayerImplInternal.handleMessage(ExoPlayerImplInternal.java:367)
                 at android.os.Handler.dispatchMessage(Handler.java:98)
                 at android.os.Looper.loop(Looper.java:154)
                 at android.os.HandlerThread.run(HandlerThread.java:61)
                 at com.google.android.exoplayer2.util.PriorityHandlerThread.run(PriorityHandlerThread.java:40)
                 at InfoAboutApp.VersionCode(numberVersionCode:1047)

  @Override
  public void releaseSource() {
    playlistTracker.release();
    playlistTracker = null;
    sourceListener = null;
  }

[ojw28]

Yup, we will do this. Thanks!