Media: Make sure mVolumeController is not null

* mVolumeController is throwing NPEs all over the place in this class, which
  causes apps like Chromecast to shit the bed when using Google Play Music
  and/or Google Play Movies
* Catch additional exception on try/catch already in place and throw in a null
  check to prevent apps from crashing until null mVolumeController is rectified

Change-Id: I7a883aa85256d5dc6af6f37978676b136cb40d0d
Signed-off-by: Brandon McAnsh <brandon.mcansh@gmail.com>