`AudioTrackPositionTracker.pause` "re-arms" the event, to ensure it
fires again when playback resumes. However the `AudioTrack` position
advances by about 100ms **after** `AudioTrack.pause()`, which
consistently causes the event to fire immediately after pausing (and
then **not** after a subsequent resumption).
This change checks whether the `AudioTrack` is paused before firing
the event, to avoid this spurious trigger.
PiperOrigin-RevId: 704759929
c377a34a5a