Improve AudioTrack offload timestamp startup glitch detector

New or existing glitch behavior for Nexus 5 offload audio:
we receive several 0 timestamps,
then we get a stale timestamp (very large),
then a few ms later we get a correct nonzero timestamp.

We attempt to hide the glitch because the retrograde timestamp
correction makes the glitch "sticky".

Bug: 21633313
Change-Id: I39153af718c151f9435e7d315651a811f72743da