edx/edx-platform — pull request #2107 by polesye (2014-01-08 10:19:41+00:00)
Title: Fix show answer button for ImageResponse.

In this PR `show answer` button is fixed ([BLD-633](https://edx-wiki.atlassian.net/browse/BLD-633)).
Frontend didn't take into account that value returned from backend could be empty.

@jmclaus please review.