DO NOT MERGE - audio flinger: fix fuzz test crash

Clear output stream pointer in duplicating thread
when the main output to which it is attached is closed.

Also do not forward master mute and volume commands to
duplicating threads as this is not applicable.

Also fix logic in AudioFlinger::primaryPlaybackThread_l()
that could accidentally return a duplicating thread.
This never happens because the primary thread is always
first in the list.

Bug: 20731946.
Change-Id: Ic8869699836920351b23d09544c50a258d3fb585
(cherry picked from commit f6870aefc5e31d4220f3778c4e79ff34a61f48ad)
3 files changed