core: prevent calling catalog with an empty list

Folder_getDeleteObjectList could do an extra paranaoïa check that the
caller did not pass an empty list of uids, because this would cause the
script to iterate on the full catalog table.

product/ERP5/bootstrap/erp5_core/SkinTemplateItem/portal_skins/erp5_core/Folder_getDeleteObjectList.py

@@ -10,6 +10,6 @@ if context.getPortalType() == 'Preference':
   return result
 else:
   # kw can contain limit, sort_on and similar runtime information
-  object_list = [x.getObject() for x in context.portal_catalog(uid=uid, **kw)]
+  object_list = [x.getObject() for x in context.portal_catalog(uid=uid or -1, **kw)]
   # only docs WITHOUT relations can be deleted
   return [x for x in object_list if x.getRelationCountForDeletion() == 0]