Make blame UI recover gracefully if Identities haven't been built yet for a commit
See PHI1014. We may not have Identities if you race the import pipeline, or in some other cases which are more "bug" / "missing migration"-flavored.
Load the commit data so we can fall back to it if we don't have identities.
- Wiped out all my identities with UPDATE ... SET authorIdentityPHID = NULL WHERE ....
- Before change: blame fataled with Attempting to access attached data on PhabricatorRepositoryCommit (via getCommitData()), but the data is not actually attached..
- After change: blame falls back gracefully.
- Restored identities with bin/repository rebuild-identities, checked blame again.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D19958