Fixed video not playing after changing speed to anything other than 1.

BLD-1221

On Firefox, if we change default video speed anything other than 1x, video will not play.

Ticket Link: https://openedx.atlassian.net/browse/BLD-1221
@polesye In ```updatePlayTime()``` there is  ```sjson.search()``` is called on time which is stopped responding when time is undefined.