Fullscreen command / button not up to date

[jinixx]

To replicate the problem, follow steps below:

1. go into fullscreen with Chrome Readium's fullscreen button while viewing epub
2. click on the video fullscreen toggler on the video ui in the epub content (shows video only in fullscreen)
3. exit video fullscreen
4. Readium exited fullscreen as well, but Readium's own fullscreen button is still on fullscreen, and so unable to enter fullscreen mode with Readium until window refresh