Fix for 2091

[marcusbritanicus]

No description provided.

[tsujan]

When both task-bars are set to show only windows on their own screens:

If a window is started on a screen, it'll be shown only on its task-bar, as expected. But if the window is moved to the other screen, the behavior will be totally erratic and could result in no task button after some movements between screens.

I guess the problem is in LXQtTaskbarWlrootsBackend::isWindowOnScreen.

EDIT: The problem was in LXQtTaskbarWlrootsBackend::onOutputsChanged: it should emit a geometry change.

Side note:
I'd be very grateful if you give good titles to PRs and refer to their corresponding issues in their main comments by using "closes" or "fixes". The reason is that a title like this will make it hard to make a changelog later.

[tsujan]

There's another problem not related to what I mentioned above:

LXQtTaskbarWlrootsWindow::outputsChanged should be disconnected appropriately on some occasions. Please see where the slot LXQtTaskbarWlrootsBackend::onStateChanged is disconnected in the code.

[tsujan]

OK, I fixed all problems, but since this PR isn't made inside LXQt, I can't add the fixes here. So, I merge it and will make another PR.

Thanks again for writing the core codes, without which we couldn't have Wayland support in lxqt-panel. Please keep up the good work!

[tsujan]

The PR is here: #2291