viewSelector: Ignore key-presses during non-overview modals

Since commit 0c807bddaf, 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

js/ui/viewSelector.js

@@ -249,6 +249,11 @@ const ViewSelector = new Lang.Class({
     },
 
     _onStageKeyPress: function(actor, event) {
+        // Ignore events while anything but the overview has
+        // pushed a modal (system modals, looking glass, ...)
+        if (Main.modalCount > 1)
+            return false;
+
         let modifiers = event.get_state();
         let symbol = event.get_key_symbol();