Don't call show() inside of QWidget, as that might make the window
fullscreen due to QStyleHints::showIsFullScreen().
This regression was introduced earlier when QWidget::show() gained
support for the hint. No auto test caught the problem, as the
affected platforms (EGL and QNX) are not CI-tested.
Change-Id: I647c2362ac5b53ced562f1d77848552cc122fba0
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>