run kmail or falkon, then run kcmshell5 fonts, change font size
ASSERT: "!d->offscreenWindow->handle()" in file /d/qt/5/kde/qtdeclarative/src/quickwidgets/qquickwidget.cpp, line 1014
Apparently that QQuickWindow should not be create()d so calling winId()
unconditionally here is a bad idea, skip non-native windows.