Do not draw on the backingstore DC when drawing
to a pixmap. Access the paintdevice for checking via
the QPaintEngine since QPainter returns the clipdevice,
which is a widget.
Fix warning about accessing handle of 0-window in the
test.
Task-number: QTBUG-24183
Change-Id: Ie91ea6ab9d09528c7ec1d35633f9a0ee667719b1
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
099029a342