use hasattr when cleaning up old ParallelListField

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@6494 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/ParallelListField.py

@@ -253,10 +253,8 @@ class ParallelListField(ZMIField):
       })
       hash_list.append(default_sub_field_property_dict)
     # XXX Clean up old ParallelListField
-    try:
+    if hasattr(self, 'sub_form'):
        delattr(self, 'sub_form')
-    except KeyError:
-      pass
     return hash_list
 
   security.declareProtected('Access contents information', 'get_value')