The queried media duration for gstreamer isn't ready at the beginning.
Instead of deactivate the audio node immediately after querying the
duration, schedule to update the media duration and use the updated
duration to schedule deactivation.

Change-Id: I8bfa69377fbc18b21baf48bc293d2d0853e8805a
Reviewed-on: https://gerrit.libreoffice.org/68451
Tested-by: Jenkins
Reviewed-by: Mark Hung <marklh9@gmail.com>