Add SortIndex propertysheet on URL, as it is required for defining sort index.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@23477 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Url.py

@@ -105,6 +105,7 @@ class Url(Coordinate, Base, UrlMixIn):
   property_sheets = (   PropertySheet.Base
                       , PropertySheet.SimpleItem
                       , PropertySheet.Url
+                      , PropertySheet.SortIndex
                       )
 
   security.declareProtected(Permissions.AccessContentsInformation,