AudioTrack: Enforce worker thread join in dtor

Ensure that the AudioTrackThread is joined in dtor. In some
cases if the dtor was called while the worker thread was in
restoreTrack_l() (which had an error due to audioserver restart)
the mStatus check incorrectly prevented join.

Test: atest CtsMediaAudioTestCases
Test: YT playback and killing audioserver
Test: atest test_callback_race
Bug: 333897807
Change-Id: I144710cb9865d45508d2f97402f748dad7e63a07