When requesting audio focus and linkToDeath() threw a
RemoteException, AudioService was only logging a warning, and
was still changing the focus, with a non-null death handler.
The change first check that linkToDeath() didn't fail, and only
then proceeds to change the focus (dispatch focus change
notification, updates the focus stack, and updates the remote
controls).
Change-Id: I0b96dd3c6e924d93f419880349d49f8b360b110b
baf674eedd