fix for glib critical errors when closing an mdi child

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51660 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/menu.cpp

@@ -989,12 +989,13 @@ wxMenu::~wxMenu()
    {
        // see wxMenu::Init
        g_object_unref(m_menu);
-       g_object_unref( m_accel );
 
        // if the menu is inserted in another menu at this time, there was
        // one more reference to it:
        if ( m_owner )
            gtk_widget_destroy( m_menu );
+
+       g_object_unref(m_accel);
    }
 }