This is a more faithful implementation of more_rbsp_data().
There could be trailing null bytes in NAL units. This isn't valid per
H264 specification, but the referenced bug includes a sample where the
PPS in the avcC record includes a trailing null byte.
Workaround the problem so packager does not fail.
A similar problem is workarounded in Chrome:
https://codereview.chromium.org/1107593004Closes#418
Change-Id: I28cb8a9371945dc094f766c3e559d7a66859b451