Fix endless while loop in gap controller with bad streams

[robwalch]

This PR will...

Fix endless while loop in gap controller with bad streams where segment duration is calculated as 0 Adjust initPTS when segments have the same start time

Why is this Pull Request needed?

JS should not lock up the page when there are unmarked discontinuities and out of sync audio and video segments that result in buffer gaps or otherwise unplayable timelines.

Are there any points in the code the reviewer needs to double check?

Resolves issues:

• #7656

Checklist

• [x] changes have been done against master branch, and PR does not conflict
• [ ] new unit / functional tests have been added (whenever applicable)
• [ ] API or design changes are documented in API.md