Provide better UX when trying to view binary file from differential

Summary:
When a user selects "show raw file (right)" from the dropdown of a binary file
in differential, they should get more than a blank page.

Test Plan: Loaded a raw binary file from differential

Reviewers: tuomaspelkonen, epriestley, jungejason

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1533