Don't assert on a missing output.

Change-Id: I07cb00bde3816276db8183cac8a9c5b14875deb1
Done-with: Vesa Halttunen <vesa.halttunen@jollamobile.com>
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Override QPlatformWindow::requestActivateWindow

The default implementation assumes activation always succeeds,
which might not be the case. The override is a no-op, making
the window activation follow keyboard focus set by the compositor.

Change-Id: I95c8cd03902a5eecd3dfbfffc338ab191e1c4f71
Done-with: Mikko Harju <mikko.harju@jolla.com>
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>