There was an off-by-one error preventing proper iteration.

BUG=angleproject:1493
BUG=chromium:638323

Change-Id: I8a3907620a1503d16b039606a67fe3471f88e165
Reviewed-on: https://chromium-review.googlesource.com/380325Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>