This is a more faithful implementation of more_rbsp_data().

There are two ways this could happen despite being invalid:
  (1) H264Parser does not strip trailing null bytes from NAL units as it
      should. This is generally not a problem because the conversion to
      Annex B won't introduce them either.
  (2) There could be trailing null bytes before the Annex B conversion.
      This isn't valid (at least for PPS NAL units), but the referenced
      bug includes a sample where the PPS in the avcC record includes a
      trailing null byte.

BUG=479229

Review URL: https://codereview.chromium.org/1107593004

Cr-Commit-Position: refs/heads/master@{#381879}