.. instead of manually casted 0s.
QCOMPARE(., nullptr) was added for Qt 5.8. Make use of the new API.
In tst_qwidget.cpp, as a drive-by, change
qApp->focusWidget() -> QApplication::focusWidget()
Change-Id: I1331b8916b026d48e01534d1ed0b3d72f3f3d50c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>