Report device disconnection on audio EOS

If --no-video was set, then device disconnection was not reported. To
avoid the problem, report device disconnection also on audio
end-of-stream (EOS).

If both video and audio are enabled, then a device disconnection event
will be sent twice, but only the first one will be handled (since it
makes scrcpy exit).

Fixes #4207 <https://github.com/Genymobile/scrcpy/issues/4207>