Merge branch 'refs/heads/t/mixer'

A single patch for para_mixer which makes the subcommands which
sleep a bit more robust.

The merge conflicted due to commit d6b25bf854c1 (mixer: fade: Handle
empty mood strings gracefully) from half a year ago, but the resolution
was obvious.

Cooking for nine months.

* refs/heads/t/mixer:
  mixer: sleep/snooze: Close mixer during sleep.