Speculative fix for division by zero in Vp8EncoderImpl.

BUG=chromium:597139
R=sprang@webrtc.org

Review-Url: https://codereview.webrtc.org/2743543004 .
Cr-Original-Commit-Position: refs/heads/master@{#17167}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 144475b3286f4de5059e0333044a72faf5d0171c
2 files changed