switcherPopup: Disable hover on scrolling events

Just like with keyboard events, disable hover on scrolling events. Mouse
movements should not mess up the selection while scrolling.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/167

js/ui/switcherPopup.js

@@ -228,6 +228,8 @@ var SwitcherPopup = GObject.registerClass({
     }
 
     vfunc_scroll_event(scrollEvent) {
+        this._disableHover();
+
         this._scrollHandler(scrollEvent.scroll_direction);
         return Clutter.EVENT_PROPAGATE;
     }