Fix a stray comma on File previews
Summary:
There's a comma to the lower-left of my profile picture here:
{F248962}
This is on a page like https://secure.phabricator.com/F248948
What's happening is that some `render()` method is returning a valid result like `array($stuff, null)`. This is getting passed to JS as an array, which is implicitly `join()`'ing it into a string, adding a comma.
Instead, make sure we render these to strings on the server side before shipping them to the client.
Test Plan: No more comma on file previews.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D10974