allView: Set delegate field

DnD still relies on the _delegate field being set, so
set it.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/603

js/ui/appDisplay.js

@@ -252,6 +252,7 @@ var AllView = class AllView extends BaseAppView {
         this.actor = new St.Widget({ layout_manager: new Clutter.BinLayout(),
                                      x_expand: true, y_expand: true });
         this.actor.add_actor(this._scrollView);
+        this._grid._delegate = this;
 
         this._scrollView.set_policy(St.PolicyType.NEVER,
                                     St.PolicyType.EXTERNAL);