psi: parse PMT packets with multiple sections

[tmm1]

fixes #74

[tmm1]

Here's a real world sample where multiple table sections are provided in a single packet, and the first section is not the PMT: https://s3.amazonaws.com/tmm1/combined-pmt-tids.ts

I recently fixed a similar bug in ffmpeg's mpegts parser. You can read more about the issue here: http://ffmpeg.org/pipermail/ffmpeg-devel/2018-May/229803.html

[tmm1]

I have several more PRs I'd like to send with PMT parsing enhancements, but they would cause merge conflicts with this one so I've held off for now. Would love to see this PR merged soon.

[tmm1]

Any objections here?

[guygrigsby]

@ieckart Can I get another set of eyes here, please?

[ieckart]

looks good to me. Reviewed the code, ran the tests, and did an integration test make sure it didn't break compatibility.

[CLAassistant]

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