treeview: insert the column button css node in the right place

Insert the css node before setting a parent widget on the column button,
so the gtk_widget_set_parent won't attempt to add the css node as child
of the parent widget css node.

gtk/gtktreeview.c

@@ -11722,10 +11722,10 @@ gtk_tree_view_insert_column (GtkTreeView       *tree_view,
 					    column, position);
   tree_view->priv->n_columns++;
 
-  _gtk_tree_view_column_set_tree_view (column, tree_view);
-
   gtk_tree_view_update_button_position (tree_view, column);
 
+  _gtk_tree_view_column_set_tree_view (column, tree_view);
+
   if (gtk_widget_get_realized (GTK_WIDGET (tree_view)))
     {
       GList *list;