Summary:
Fixes T12097. In D16413, I simplified this code but caused us to load the //commit's// projects instead of the //repository's// projects, which is incorrect.

Normally, commits don't have any project tags when Herald evaluates, so using the commit's projects is generally meaningless.

Test Plan:
  - Tagged a repository with `#X`.
  - Created a Herald object rule for commits with `#X` as the object ("Always ... do nothing.")
  - Ran a commit from the repository.
  - Before patch: rule failed to evaluate.
  - After patch: rule evaluated and passed.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12097

Differential Revision: https://secure.phabricator.com/D17179