CRAS: audio_thread - Only skip mixing a stream if it is empty.
CRAS: audio_thread - Only skip mixing a stream if it is empty.

Don't skip mixing a stream just because it times out.  If there are
still some samples, mix them.

BUG=none
TEST=play music, youtube, and pandora.

Change-Id: I34249f5d6b865b72a45f3678c1770cfacd32af29
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/185665

drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd