Fix H.264 start code position search.
Fix H.264 start code position search.

This will address incorrect start code search
in a sequence like 00 00 00 00 00 01.
Thanks Noah.

R=noahric@chromium.org, wzh@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/41159004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8639}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: dc08a230da9f6bb21299b01e4e0cbf12b11e0605

dcpang/fatline-libjingle,sippet/talk,dcpang/fatline-libjingle,sippet/talk,dcpang/fatline-libjingle,sippet/talk,sippet/talk,dcpang/fatline-libjingle,dcpang/fatline-libjingle,sippet/talk