This should fix any potential out of bounds reads/writes.

BUG=chromium:660854

Change-Id: Iffa00e4551d7362115cbf023a09b1d0e15f724c8
Reviewed-on: https://chromium-review.googlesource.com/405816
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>