Make blame UI recover gracefully if Identities haven't been built yet for a commit

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

src/applications/diffusion/controller/DiffusionBlameController.php

@@ -25,6 +25,9 @@ final class DiffusionBlameController extends DiffusionController {
         ->withRepository($repository)
         ->withIdentifiers($identifiers)
         ->needIdentities(true)
+        // See PHI1014. If identities haven't been built yet, we may need to
+        // fall back to raw commit data.
+        ->needCommitData(true)
         ->execute();
       $commits = mpull($commits, null, 'getCommitIdentifier');
     } else {