xwayland: fix issue with panel getting stuck offscreen

xwayland: fix issue with panel getting stuck offscreen

For unknown reasons, XWayland surfaces that are completely offscreen
seem not to generate commit events. In rare cases, this can prevent an
offscreen window from moving onscreen (since we wait for a commit event
that never occurs). As a workaround, move offscreen surfaces
immediately.

This fixes an issue that I can reproduce by having qmpanel displayed on
a (larger) external monitor, then undocking the laptop so that qmpanel
requests a simultaneous move+resize to the (smaller) laptop display.