[HLSTree] Fix missing codec for media playlist

[CastagnaIT]

Description

A kind of regression,
i remember now that when i had done the big parsers rework i had intentionally removed the codec property set here to try investigate on this weird parser implementation but i also forgot to readd it

to full fix this require a big rework of HLS parser to act like the other parsers
and maybe there is also the possibility to get rid of prepareRepresentation and other things around this...
this requires some study and time, one of many pending todo's (now add to roadmap)

Motivation and context

fix #1327

How has this been tested?

http://devimages.apple.com/iphone/samples/bipbop/gear1/prog_index.m3u8

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• I have read the Contributing document
• My code follows the Code Guidelines of this project
• My change requires a change to the Wiki documentation
• I have updated the documentation accordingly