This call cannot fail, but needs cleanup if others fail.  By moving it
to the end, we eliminate some cleanup.

Moved code from AudioOutputControl::InternalOpen2().

struct AudioOutput should not know or care about multi-threading.

Prepare for moving the AudioOutputSource to class AudioOutputControl.

That function is "noexcept".

This allows removing the "base.pause" check from the JACK output
plugin, and will allow removing similar accesses from other plugins.