builder-tool: Handle layout properties gracefully

If there are already layout properties in the ui
file, we shouldn't crash, even if --3to4 is given.

gtk/tools/gtk-builder-tool-simplify.c

@@ -438,6 +438,9 @@ get_class_name (Element *element)
 
   if (g_str_equal (parent->element_name, "packing"))
     parent = parent->parent->parent; /* child - object */
+  else if (g_str_equal (parent->element_name, "layout"))
+    parent = parent->parent->parent->parent; /* object - child - object */
+
 
   if (g_str_equal (parent->element_name, "object"))
     {