[gtk+] tree model sort: Fix initial default sort func

[Matthias Clasen <matthiasc src gnome org>]

commit 42369e31e2ed127abac6a9cd06ac64e27a6e398b
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Jan 16 18:15:13 2018 -0500

    tree model sort: Fix initial default sort func
    
    gtk_tree_sortable_has_default_sort_func should return
    FALSE initially.

 gtk/gtktreemodelsort.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtktreemodelsort.c b/gtk/gtktreemodelsort.c
index 336f796..761e01f 100644
--- a/gtk/gtktreemodelsort.c
+++ b/gtk/gtktreemodelsort.c
@@ -1768,7 +1768,7 @@ gtk_tree_model_sort_has_default_sort_func (GtkTreeSortable *sortable)
 {
   GtkTreeModelSort *tree_model_sort = (GtkTreeModelSort *)sortable;
 
-  return (tree_model_sort->priv->default_sort_func != NULL);
+  return (tree_model_sort->priv->default_sort_func != NO_SORT_FUNC);
 }
 
 /* DragSource interface */