Ensure MediaRouter.setMediaSessionCompat(null) does not crash

While MediaRouter.setMediaSession() works with a null MediaSession,
the Compat version failed on all API14+ devices with a
NullPointerException. Ensure that passing in a null
MediaSessionCompat is handled correctly - removing any existing
RemoteControlClient (on API14-20 devices) and passing onto
setMediaSession() on API21+ devices.

BUG: 21035180
Change-Id: Ie5e11ca043fc4b6ce072eede7ba202985e28f0cb
1 file changed