aaudio: fix hang in client when audioserver dies

Fix timeout detection so that callback thread can die.
Prevent AAudioBinderClient singleton from getting deleted,
which caused a subsequent lock on a dead object to hang.

Bug: 64988439
Test: "write_sine -m2 -pl" and "adb shell killall audioserver"
Change-Id: I044bce385b66e69007d1997f051c9d6c042b7871