hls-mp4: fix uint32's parsing

[kanongil]

Description of the Changes

The uint32 parsing logic actually produces int32 values, due to use of bitwise operators. This means that negative values can be parsed, which can cause the processing to fail.

I discovered this, when debugging a stream that suddenly stopped working, while spouting negative timestamp values into the debug log. Specifically, it was the parsing of the lower bits of a version==1 tfdt box. I fixed the other instances as well for good measure.

CheckLists

• changes have been done against master branch, and PR does not conflict
• no commits have been done in dist folder (we will take care of updating it)
• new unit / functional tests have been added (whenever applicable)
• Travis tests are passing (or test results are not worse than on master branch :))
• API or design changes are documented in API.md

[mangui]

thanks @kanongil
LGTM, merging