[seahorse] Fix for GTK+ 3.0 filter model changes.

[Stefan Walter <stefw src gnome org>]

commit 5705c613665238aa3566f937c74628be4d1b153d
Author: Stef Walter <stefw collabora co uk>
Date:   Fri Sep 2 11:40:19 2011 +0200

    Fix for GTK+ 3.0 filter model changes.
    
     * seahorse_set_model_iter_nth_child gets called with NULL iter.

 libseahorse/seahorse-set-model.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/libseahorse/seahorse-set-model.c b/libseahorse/seahorse-set-model.c
index 54ae425..6944092 100644
--- a/libseahorse/seahorse-set-model.c
+++ b/libseahorse/seahorse-set-model.c
@@ -568,7 +568,7 @@ seahorse_set_model_iter_nth_child (GtkTreeModel *tree_model, GtkTreeIter *iter,
 	GNode *node;
 
 	g_return_val_if_fail (SEAHORSE_SET_MODEL (tree_model), FALSE);
-	node = node_for_iter (pv, parent);
+	node = parent ? node_for_iter (pv, parent) : pv->root_node;
 	g_return_val_if_fail (node != NULL, FALSE);
 	node = g_node_nth_child (node, n);
 	if (node == NULL)