AudioFlinger: do not enter standby on offload stream when underrunning

When an offloaded track has been underrunning long enough for the
stream to enter standby, do not enter standby: entering standby will
release DSP resources and cause problems if we resume after recovering
from the underrun.

Bug: 322874013
Fixes: 333970720
Test: offload playback test with forced underrrun
Change-Id: I942fd3f401c226977f4f0684ed0e5a7a03db735d