Make blame UI recover gracefully if Identities haven't been built yet for a commit master
Summary: 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. Test Plan: - 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. Reviewers: amckinley Reviewed By: amckinley Differential Revision: https://secure.phabricator.com/D19958