Fix crash parsing malformed rtp packet
where header extesnsion size mismatch expected.

BUG=chromium:620242
R=asapersson@webrtc.org

Review URL: https://codereview.webrtc.org/2067793003 .

Cr-Original-Commit-Position: refs/heads/master@{#13170}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 5a45fe6fd7a509fb4c3a9b09cdbd2278055f1d4c
2 files changed