Workflow.py: fix a confusion between list and dict.

product/ERP5Workflow/Document/Workflow.py

@@ -206,7 +206,7 @@ class Workflow(IdAsReferenceMixin("", "prefix"), XMLObject):
       '''
       if name == self.getStateVariable():
           return 1
-      vdef = self.objectValues(portal_type='Variable').get(name, None)
+      vdef = self.getVariableValueList().get(name, None)
       if vdef is None:
           return 0
       return 1