mixer: don't show softvol neutral marker on OSD if not using softvol

Also fix the comment on the softvol field.
audio: fix busy loop when seeking while paused

When playing paused, the amount of decoded audio is limited to a small
amount (1 sample), because we don't write any audio to the AO when
paused. The small amount could trigger the case of the wanted audio
being too far in the future in the PTS sync code, which set the audio
status to STATUS_DRAINING, which in turn triggered the EOF code in the
next iteration. This was ok, but unfortunately, this triggered another
retry in order to check resuming from EOF by setting the status to
STATUS_SYNCING, which in turn lead to the busy loop by alternating
between the 2 states. So don't try resyncing while paused.

Since the PTS syncing code also calls ao_reset(), this could cause the
pulseaudio daemon to consume some CPU time as well.

This was caused by commit 33b57f55. Before that, the playloop was merely
run more often, but didn't cause any problems.

Fixes #1288.