Directly use WorkflowTool to access time value.

Mixed commit:

  43b1ae1b
  2f05fe1b

product/ERP5Type/Base.py

@@ -3122,11 +3122,12 @@ class Base( CopyContainer,
       pass
     else:
       max_date = None
-      for history in history_list.itervalues():
-        try:
-          date = history[-1]['time']
-        except (IndexError, KeyError):
-          continue
+      portal_workflow = getToolByName(self.getPortalObject(), 'portal_workflow')
+      getStatusOf = portal_workflow.getStatusOf
+      for key, _ in history_list.iteritems():
+        status = getStatusOf(key, self)
+        if status is not None and status.has_key('time'):
+          date = status['time']
           if date > max_date:
             max_date = date
       if max_date: