Modal GtkPopover should not pass key presses to the window, nor allow accels be activated
When a modal GtkPopover is attached to a widget, which is part of he window, and both the widget and the window have key-press-event
handlers and the window has also the accels registered, then neither the key-press-event
handlers nor the accels should be activated while this modal GtkPopover is shown. Otherwise it can lead to crash, among other things like unexpected behavior.