Fix null pointer arithmetic, re-enable -Wnull-pointer-arithmetic

Bug: 766891
Change-Id: Ib8cf38fb63d9494f21462ab55ce361775b107322
Reviewed-on: https://chromium-review.googlesource.com/c/1390003
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#619731}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 2fcaf0a1e55b010353bcdee64e14911a03010b68
4 files changed