Fix an issue where we may "min()" an empty array when viewing a revision with no changesets
Ref T13667. When a revision's diff has no changesets (usually because Diffusion performed an automatic update with an empty commit), the UI currently tries to "min()" an empty array and fatals.
Handle this case properly.
- Created a revision with a diff with no changesets ("git commit --allow-empty" + copy-paste into web UI).
- Viewed revision.
- Before: "min()" fatal.
- After: UI isn't perfect, but works without fataling.
Maniphest Tasks: T13667
Differential Revision: https://secure.phabricator.com/D21760