prevent IndexError if there is no latest version

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@39360 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/Document.py

@@ -469,8 +469,8 @@ class Document(DocumentExtensibleTraversableMixin, XMLObject, UrlMixIn, CachedCo
         return result_list[0].getObject()
       except IndexError:
         return None
-    else:
-      first = result_list[0].getObject()
+    elif result_list:
+      first =  result_list[0].getObject()
       in_original = None
       for record in result_list:
         document = record.getObject()