Update a2dp state to not playing while quitting the state machine

- Fix a race condition for a2dp while turning off Bluetooth.
- Audio state won't be updated if A2dpService stop before stack
  report audio state change.
- Update audio state to not playing if it is playing and the
  state machine is quitting.

Bug: 79911521
Test: manual test, turn off Bluetooth while a2dp is playing
Change-Id: I09c4e062fd2205abf57c25ca44cba27088ebf5e5