Sound hardware preferences pane allows OK when errors exist

This is a greater problem in the preferences, not just the sound hardware pane. No pane (dlgpref{eq,sound,...}) is able to disable the OK button owned by dlgpreferences, or really communicate with it at all in any meaningful way.

Not that disabling an OK button doesn't have huge usability implications of its own, I'd think most HIG groups would find it high treason.

This still happens in Mixxx 2.3 alpha

I think this can be resolved rather "easily", no need to violate HIG:

1. in the preferences main dialog, intercept the
  QDialogButtonBox::accepted signal and accept() the dialog only if
  okayToclose of each pref page is true (default)
2. in DlgPrefSound::slotApply, set okayToClose to true only if
  SoundDeviceError is SOUNDDEVICE_ERROR_OK

Does that makes sense?

https://github.com/mixxxdj/mixxx/blob/828a189b045050ca6ad5aa053e528e92ce0b8653/src/preferences/dialog/dlgpreferences.cpp#L408-L442

We have two issues, one is a faulty configuration Mixxx knows.
This can be solved by returning to the preferences after the error dialog appears.

A future version may instantly mark the fault fields red that the user is informed before hitting OK.

The other issue are unknown faults that only appear when the config is actually applied. I think we already have a loop returning to the preferences at start up. Maybe we can do similar.

I currently suffer an issue with Pipewire and the Mixxx default using JACK, that Mixxx stalls after pressing OK. I have not yet reported a bug yet, because Pipewire is not official supported with Ubuntu Focal, so it might be my fault. But in any case would is be preferred to have a common timeout solution to cover such issues.

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/6077