shell: Avoid reserving a screen edge if no surface role has been created yet
Check QWindow::isExposed() as in other places. If the surface role object has been created, isExposed() will return true.
(cherry picked from commit 472c5790)
Check QWindow::isExposed() as in other places. If the surface role object has been created, isExposed() will return true.
(cherry picked from commit 472c5790)