viewSelector: Ignore key-presses during non-overview modals

viewSelector: Ignore key-presses during non-overview modals

Since commit 0c807bddaf4d, the run dialog no longer handles Escape
key presses itself but uses the action key mechanism of modal dialogs.
As the latter uses key-release events, our own handling of the Escape
key runs on key-press.
Fix this by bailing out early if anything has pushed a modal in addition
to the overview (like system modals, looking glass, ...).

https://bugzilla.gnome.org/show_bug.cgi?id=688196