Fix a pb if realPeriodId is "".

[jeremco]

Using 4K stream (https://dash.akamaized.net/akamai/streamroot/050714/Spring_4Ktest.mpd)
In the manifest, period id value is "". Then the method DashAdapter::getAdaptationForMediaInfo returns null, because of the test (!mediaInfo.streamInfo.id).

This PR fixes the pb by checking length of id

[epiclabsDASH]

This same issue is fixed, in a different way, in #2140 (commit b85802b).

This is open to discussion but, IMHO, I prefer this approach: assigning an id to whatever period definition that didn't indicate one or that let's it empty (assuming that let's it empty is equivalent do don't set an id).

@nicosang, @jeremco, what do you think?

[nicosang]

Hi @epiclabsDASH,

according to me, both modifications are not opposite. Indeed, @jeremco 's modification seems to be better. Yet, a unit test of the getAdaptationForMediaInfo function could failed with an id equals to ''. So, both modifications may remain so.

Nicolas

[epiclabsDASH]

Ok. We will be testing a situation that is never going to happen (id equals '') but been strict it is ok to include that kind of test scenario as part of the unit tests.

@nicosang, agree with you.

[nicosang]

I do not agree with you, it's not a situation that is never going to happen. For instance, a user can call an attachSource with a already parsed manifest..... ;-)

[epiclabsDASH]

Touché! Good point, you are right ;)