status: don't show 'Show Keyboard Layout' on the login screen

It does not make a great amount of sense to have this function
on the login screen. And worse, it does not work, since the greeter
is currently a modal dialog, so interaction with the opening
window is impossible.

https://bugzilla.gnome.org/show_bug.cgi?id=659164

js/ui/status/keyboard.js

@@ -67,11 +67,13 @@ XKBIndicator.prototype = {
 
         this._sync_config();
 
+        if (global.session_type == Shell.SessionType.USER) {
             this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
             this.menu.addAction(_("Show Keyboard Layout"), Lang.bind(this, function() {
                 Main.overview.hide();
                 Util.spawn(['gkbd-keyboard-display', '-g', String(this._config.get_current_group() + 1)]);
             }));
+        }
         this.menu.addSettingsAction(_("Region and Language Settings"), 'gnome-region-panel.desktop');
     },