[glade3] * plugins/gtk+/glade-column-types.c: Fixed crash when user performs Drag'n'Drop of < enter column

[Tristan Van Berkom <tvb src gnome org>]

commit 52330855cb41cae02a395792c0cfd6f3a9aaa725
Author: Tristan Van Berkom <tristan van berkom gmail com>
Date:   Sun Jan 9 17:25:26 2011 +0900

    	* plugins/gtk+/glade-column-types.c: Fixed crash when user performs Drag'n'Drop of
    	< enter column here > and no columns are yet added (fixes bug 633943).

 ChangeLog                         |    3 +++
 plugins/gtk+/glade-column-types.c |    7 ++++++-
 2 files changed, 9 insertions(+), 1 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index c8a20db..55dee14 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -43,6 +43,9 @@
 	* src/glade-window.c: Fixed use of uninitialized variables in warning messages,
 	bug 634325, fix by Alex Merry.
 
+	* plugins/gtk+/glade-column-types.c: Fixed crash when user performs Drag'n'Drop of
+	< enter column here > and no columns are yet added (fixes bug 633943).
+
 2011-01-08  Tristan Van Berkom <tristanvb openismus com>
 
 	* gladeui/glade-utils.[ch], gladeui/glade-widget.c, gladeui/glade-builtins.c,
diff --git a/plugins/gtk+/glade-column-types.c b/plugins/gtk+/glade-column-types.c
index ce124f3..114120c 100644
--- a/plugins/gtk+/glade-column-types.c
+++ b/plugins/gtk+/glade-column-types.c
@@ -435,7 +435,12 @@ columns_changed_idle (GladeEditorProperty * eprop)
   property = glade_editor_property_get_property (eprop);
 
   glade_property_get (property, &columns);
-  g_assert (columns);
+
+  /* This can happen when the user performs DnD and there
+   * are no columns yet */
+  if (!columns)
+    return FALSE;
+
   columns = glade_column_list_copy (columns);
 
   if (gtk_tree_model_get_iter_first