Fix retry icon on iOS when connection is down

Summary: Related: https://github.com/Khan/khan-mobile/commit/c8ae9ecbe0f39b99d592fe9fbfc47b6c08431bb8

Test Plan:
iPad
Airplane mode on
Load video
Make sure retry icon is visible
Make sure download/share icons are visible

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D7240