Fix a fatal on the file info screen

Summary: D1354 added a query for a possibly-empty list -- only show the table if
there are transformations.

Test Plan: Reloaded a previously-fataling page, no fatals. Viewed a file with
transformations, got a list.

Reviewers: davidreuss, btrahan, jungejason

Reviewed By: davidreuss

CC: aran, davidreuss

Differential Revision: https://secure.phabricator.com/D1414