[gdl] Fix bgo #680655 - test-dock crashes

[Sebastien Granjoux <sgranjoux src gnome org>]

commit abc3147e48544a90a60f6e2e40ad7f8cf99ccef4
Author: SÃbastien Granjoux <seb sfo free fr>
Date:   Sun Jul 29 17:32:49 2012 +0200

    Fix bgo #680655 - test-dock crashes

 gdl/gdl-dock.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gdl/gdl-dock.c b/gdl/gdl-dock.c
index 57b6c7d..9a8e14b 100644
--- a/gdl/gdl-dock.c
+++ b/gdl/gdl-dock.c
@@ -1306,9 +1306,11 @@ gdl_dock_add_item (GdlDock          *dock,
     g_return_if_fail (dock != NULL);
     g_return_if_fail (item != NULL);
 
-    /* Check if a placeholder widget already exist */
+    /* Check if a placeholder widget already exist in the same dock */
     placeholder = gdl_dock_master_get_object (GDL_DOCK_OBJECT_GET_MASTER (dock), GDL_DOCK_OBJECT (item)->name);
-    if ((placeholder != NULL))
+    if ((placeholder != NULL) && 
+        gdl_dock_item_is_closed (placeholder) &&
+        (gdl_dock_object_get_toplevel (placeholder) == dock))
         parent = gdl_dock_object_get_parent_object (placeholder);
 
     if (parent && gdl_dock_object_child_placement (parent, placeholder, &place))