overview: Don't pick for every overlay

Don't do an individual hover fixup for every window overlay, instead
just use the new global.sync_hover() to fix up hovers once we have
finished showing the overview.

Based on a patch from Adel Gadllah <adel.gadllah@gmail.com>

https://bugzilla.gnome.org/show_bug.cgi?id=638613

js/ui/overview.js

@@ -690,6 +690,7 @@ Overview.prototype = {
             this._animateNotVisible();
 
         this._syncInputMode();
+        global.sync_pointer();
     },
 
     _hideDone: function() {