[gnome-shell] popupMenu: Fix setting ImageMenuItem's icons via strings

[Florian Müllner <fmuellner src gnome org>]

commit c12da66da8b82f762c47109735391488ca2cfee9
Author: Florian Müllner <fmuellner gnome org>
Date:   Mon Oct 16 00:09:52 2017 +0200

    popupMenu: Fix setting ImageMenuItem's icons via strings
    
    Commit 28ca96064bcb added support for setting PopupImageMenuItem's icons
    via GIcons as well as via strings. However as the check whether an object
    implements the GIcon interface only works on GObjects, specifying an icon
    name was broken. Fix that to actually allow both strings and GIcons.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=789018

 js/ui/popupMenu.js |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/js/ui/popupMenu.js b/js/ui/popupMenu.js
index d00132f..cb975f5 100644
--- a/js/ui/popupMenu.js
+++ b/js/ui/popupMenu.js
@@ -405,7 +405,7 @@ var PopupImageMenuItem = new Lang.Class({
 
     setIcon: function(icon) {
         // The 'icon' parameter can be either a Gio.Icon or a string.
-        if (GObject.type_is_a(icon, Gio.Icon))
+        if (icon instanceof GObject.Object && GObject.type_is_a(icon, Gio.Icon))
             this._icon.gicon = icon;
         else
             this._icon.icon_name = icon;