This seems to be a merge error. The if moved down by a few lines and
now actually implements the bounds check instead of bailing out.
Taking it out revealed a bug where we were trying to access the lowest
8 bits on a register where this is not allowed on ia32, thus a few
more changes were needed in this CL.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Ib1ef131a12df050302ae50115493a1fcd8323fe5
Reviewed-on: https://chromium-review.googlesource.com/852734Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50422}