R1:11c5638832c2

Fix some error log issues with uninitialized commit/revision lists

Summary:
Fixes T12679. Reproduction steps appear to be:

- As a logged-out user, view revision list or commit list.
- Enable bucketing by action required.
- Before patch: `foreach (null as ...)` causes error spew.
- After patch: `foreach (array() as ...)` works great.

Test Plan:
- Reproduced issue by following steps above in Differential (revisions) and Diffusion (audits/commits).
- After patches, no more errors in the log.