Workflow.py: fix variable for_status checking.

product/ERP5Workflow/Document/Workflow.py

@@ -657,7 +657,7 @@ class Workflow(IdAsReferenceMixin("", "prefix"), XMLObject):
     for vdef in self.objectValues(portal_type='Variable'):
       id = vdef.getId()
       id_no_suffix = vdef.getReference()
-      if vdef.for_status == 0:
+      if not vdef.for_status or vdef.for_status == 0:
         continue
       expr = None
       if id_no_suffix in state_values: