Missing user does bad things on issue update

JRA-12360 corrected JIRA so that it can still display an issue even if it references a user that is not longer in the crowd database. However, bad things happen if you attempt to edit the issue, either singly or in bulk, and it prevents you from correcting the missing user problem.
I'm attaching a couple of stack traces:

1. What happens when you try to edit an issue assigned to or reported by a non-existent user.
2. What happend after the user is recreated in Crowd.

We should also test if anything bad happens with comments by non-existant users.