appsMenu: Fix initial visibility of "Details" item

It is only supposed to be visible when Software is installed, but
we currently only update the visibility on changes.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/989

js/ui/panel.js

@@ -110,9 +110,14 @@ class AppMenu extends PopupMenu.PopupMenu {
         });
 
         this._appSystem.connect('installed-changed', () => {
+            this._updateDetailsVisibility();
+        });
+        this._updateDetailsVisibility();
+    }
+
+    _updateDetailsVisibility() {
         let sw = this._appSystem.lookup_app('org.gnome.Software.desktop');
         this._detailsItem.actor.visible = (sw != null);
-        });
     }
 
     isEmpty() {