Vlad Zahorodnii authored Jun 16, 2020 and Vlad Zahorodnii committed Jun 25, 2020

Depending on the current focus stealing prevention level, it's possible
for kwin to call XSetInputFocus() on a window that already has the input
focus. In which case, we won't receive the corresponding FocusIn event
and the client will remain inactive from kwin's perspective even though
it isn't.

In order to work around this issue, we can move the input focus to the
null window. By doing so, it's guaranteed that we're going to receive
the matching FocusIn event for the client.

This commit indirectly fixes a bug where fullscreen games are displayed
below panels.