aaudio: prevent busy loop on shared stream standby

Avoid doing a wait with an extremely high duration.
It does not wait so the loop spins.

Add explicit call to isStandbyImplemented() to
avoid having to use the extremely high duration.

Bug: 344664088
Test: See bug for details.
Test: adb logcat | grep COMMANDS
Test: Use OboeTester to open a Shared stream
Test: Wait 10 seconds.
Test: Enter:  adb shell top
Test: Close stream.
Test: Check logcat. Number of loops should be < 10.
Flag: EXEMPT bugfix
Change-Id: I5fa641f692206a5bb4514365c07892c28e315171