MatroskaExtractor: skip track when codec id is NULL in addTracks

This is a more thorough version of commit
ea9ac8bf7f6a7ae1424c6cade64b004caa7c3681
in that it applies to both video and audio.

Bug: 17702053
Bug: 18872598
Change-Id: Idcea77bb7133ea0d02da8c484b4a0791db42740e
1 file changed