Fix Video preview

Steps to reproduce:

• Install all embedded addons.
• Navigate to Domain > Workspaces > Sample Content > Videos
• Open Keyboard.mp4
  => Storyboard available, but Preview is not.
• Click play button.
  => Video doesn't play.
  => The following errors are visible in the console:

  Failed to load resource: the server responded with a status of 404 ()
  18:14:05.181 :8080/nuxeo/ui/#!/browse/default-domain/workspaces/Sample%20Content/Videos/Keyboard.mp4:1
  Refused to execute script from 'http://localhost:8080/nuxeo/ui/scripts/babel-helpers.min.js' because its MIME type ('text/html') is not executable, and strict MIME type checking is enabled.
  

• Navigate to either of the other videos in the Videos folder, Coastline.mp4 or River.mp4.
  => Preview and Storyboard are displayed.
• Click on the play button.
  => Video plays.

Not reproduced on Firefox.