GladeWidget: fix rebuild() function

Remove object from project before extracting children since we clear up
GladeWidget back references for internal children.

Fix issue #484 "Crash with GtkRecentChooserDialog"

gladeui/glade-widget.c

@@ -2552,9 +2552,6 @@ glade_widget_rebuild (GladeWidget *gwidget)
 
   g_object_ref (gwidget);
 
-  /* Extract and keep the child hierarchies aside... */
-  children = glade_widget_extract_children (gwidget);
-
   /* Here we take care removing the widget from the project and
    * the selection before rebuilding the instance.
    */
@@ -2569,6 +2566,9 @@ glade_widget_rebuild (GladeWidget *gwidget)
       glade_project_remove_object (project, gwidget->priv->object);
     }
 
+  /* Extract and keep the child hierarchies aside... */
+  children = glade_widget_extract_children (gwidget);
+
   /* parentless_widget and object properties that refer to this widget 
    * should be unset before transferring */
   l = g_list_copy (gwidget->priv->properties);