message: Prevent exception when dettaching closed mirrored tracks
diff: @@ -157,7 +157,10 @@ class IncomingStreamTrackMirrored
  */
  attached()
  {
  - //Singal original track is attached
  + //If we are already stopped
  + if (!this.track) return;
  +
  + //Signal original track is attached
  this.track.attached();
  //Increase attach counter
  @@ -193,7 +196,10 @@ class IncomingStreamTrackMirrored
  */
  detached()
  {
  - //Singal original track is deattached
  + //If we are already stopped
  + if (!this.track) return;
  +
  + //Signal original track is deattached
  this.track.detached();
  //Decrease attach counter
  