When viewing Diffusion blame on a file which has a commit that references a Differential code review on a deleted repository, the ajax blame call fatals out.

While deleting repositories is clearly called out as a dangerous action it is sometimes a necessary one when repositories grow too large and need to be "rebooted".

fixes T13040

1. Create new repo
2. Create code review against repo
3. Land code review
4. Push code to a new repo on same instance
5. Delete old repo
6. Open blame for file
7. Blame does not open
8. Apply patch
9. Blame opens