appDisplay: Hide empty app folders

Trying to open an empty folder currently leaves the parent view in a
rather confused state. While we should look into fixing this in the
future, empty folders are not useful at all to begin with, so hide them.

https://bugzilla.gnome.org/show_bug.cgi?id=736910

js/ui/appDisplay.js

@@ -1267,6 +1267,7 @@ const FolderIcon = new Lang.Class({
             addAppId(appInfo.get_id());
         });
 
+        this.actor.visible = this.view.getAllItems().length > 0;
         this.view.loadGrid();
         this.emit('apps-changed');
     },