audio: Don't play sound effects if stream is muted

 * Stop turning on the audio hardware and playing silence.
 * Kind of annoying with certain types of Bluetooth headphones
   that don't actually play silence very well (hissssssssss).
   Not to mention power usage.

Change-Id: I6985db8710f8b0f61619ac57e8efb9e4e01cc31a
(cherry picked from commit 0e8a502ff119d285fdbbf521c45213b0b42b3d6f)