Ensure that Window::output() is always in sync with the frame geometry
plasmashell may see new output layout before kwin_x11 and move desktop windows accordingly. If that happens, the desktop windows will have old outputs in Window::output() property because the Workspace doesn't re-check outputs if the output layout changes. In order to fix the Window::output() property getting out of sync, re-check the current output after the output layout changes. It should also fix a visual glitch in the slide effect caused by EffectWindow::screen() not being correct.