When viewing a thread with no picture, load no images instead of all images

Summary:
Currently, we select every file when looking at a thread with no splash image.

(Possibly the Query stuff should try to catch this.)

Test Plan: No more `SELECT * FROM files` query.

Reviewers: chad, btrahan, vrana

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D4887