apply published state for migrations of broken comments

[thet]

For migrations of comments without a valid old_status, apply the 'published' state.

i have a situation, where in line 119 of plone.app.event.browser.migration returns None:
old_status = workflow.getStatusOf(oldchain, reply)

since i had the one_state_publication workflow for discussion items applied, i solved the issue by applying the published state to those comments.

i don't know if this is acceptable as default behavior, so please review it.
if you need more information obout the comments in question, i'm happy to help.

this is the traceback i got before my change:

2012-10-31 22:28:32 ERROR Zope.SiteErrorLog 1351718912.740.436631714231 http://localhost:8880/@@comment-migration
Traceback (innermost last):
  Module ZPublisher.Publish, line 126, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module ZPublisher.Publish, line 46, in call_object
  Module plone.app.discussion.browser.migration, line 205, in __call__
  Module plone.app.discussion.browser.migration, line 124, in migrate_replies
AttributeError: 'NoneType' object has no attribute 'get'