Shaka-player: Optional StartTime is not working properly because of invalid startTime check

[SemihGk]

Have you read the FAQ and checked for duplicate issues:
Yes
What version of Shaka Player are you using:
latest
Can you reproduce the issue with our latest release version:
yes
Can you reproduce the issue with the latest code from master:
yes

What did you do?
I sent optional startTime paramater to shaka.Player.load() method as 0, but video was not starting from currentTime = 0. After some investigation, I found some invalid checks on your code blocks that handles startTime. Please check
https://github.com/google/shaka-player/blob/master/lib/player.js#L818 .
At this line, PlayHead method recieves null instead of 0.

Also: https://github.com/google/shaka-player/blob/master/lib/media/playhead.js#L201
Same problem exists at this line as well.

After fixing this 2 line, it works well. It should be a quick fix for you since we may need this fix soon. If you prefer a PR, I do not mind to create one as well.

Thanks,
Semih.

[chrisfillmore]

To add more context: we need to be able to set a startTime of 0 in order to support restartable live content.

[TheModMaker]

Thanks for finding this, will have a fix up soon.

[joeyparrish]

Cherry-picked to v2.2.3.

[joeyparrish]

A follow-up fix (fix of the fix) has been cherry-picked to v2.2.4.