ERP5Catalog: tolerate non-set return value for ERP5Site_filterUserIdSet

set.__iadd__ does not like non-set values, but the intent of this API is
to allow just any iterable (producing strings) to be returned, so use
the more tolerant set.update method instead.

product/ERP5Catalog/CatalogTool.py

@@ -897,9 +897,9 @@ class CatalogTool (UniqueObject, ZCatalog, CMFCoreCatalogTool, ActiveObject):
         # Note: we mutate the set, so all related wrappers get (purposedly)
         # affected by this, which must happen before _getSecurityParameterList
         # is called (which happens when calling getSecurityUidDict below).
-        user_set += portal.ERP5Site_filterUserIdSet(
+        user_set.update(portal.ERP5Site_filterUserIdSet(
           group_and_user_id_set=group_and_user_id_set,
-        )
+        ))
 
       getSecurityUidDict = catalog_value.getSecurityUidDict
       getSubjectSetUid = catalog_value.getSubjectSetUid