Android: avoid crash with toplevel QGLWidget

Task-number: QTBUG-37096

Change-Id: I14db37a78314782d7b5897db946283bd0063e348
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
QQuickWidget show/hide/raise fix

Make sure the alphamask in the backingstore is updated whenever the
state of a QQuickWidget/QOpenGLWidget child changes.

Task-number: QTBUG-37062
Change-Id: Iffa80fc8993499a15bc9e773a162a3f98b81ae03
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>