Fix crash on decode found by fuzz tester.

BUG=crbug:468963
R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45859004

Cr-Original-Commit-Position: refs/heads/master@{#8858}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 79064e568ece1d89d9a7eeb8d93388823ed30a1f
2 files changed