Fix two minor issues with Pholio

Summary:
  - One bad method call.
  - One fatal when handling a mock with no images. These "can't" exist, but we have a few old ones I think and it's probably better not to fatal. We could filter the object out completely, but this doesn't seem like a bad fix?

Test Plan: Viewed `/pholio/` (although I don't think I have any imageless mocks) and viewed an outdated image.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6574