This tries to fix wrong behavior when optical cable is unplugged while spdif-output is running.

Currently, you will probably hear pops and you only get sound from internal speakers,
after you changed system volume.
(cherry picked from commit bdf858dae3bd2c81ceb2082b4c3ac36d2712d612)

Conflicts:
	modules/audio_output/auhal.c
Signed-off-by: Felix Paul Kühne <fkuehne@videolan.org>