[iOS] Completion doesn't work for videos in PiP mode.

[sergeymomot]

Steps to reproduce:

1. open any content with video
2. complete all other cards (if they are present) except the card with video
3. go to the card with the video and start playing
4. switch to PiP mode
5. exit the content (for example, to Profile or other content)
6. wait for the video to finish playing
7. go to coursework and check completion status of the content
8. Result: content will not be completed, although all the cards have been completed and the video has been watched to the end

at the same time, if you switch to PiP mode and do not leave the content, then after playing the video to the end, the content will receive status "Completed".