At the moment the implementation of LoadElemSegmentImpl is not ready
to support the loading of passive element segments into tables with
index > 0. I added a check so that we notice when somebody starts to
implement it.

R=binji@chromium.org

Bug: v8:9270
Change-Id: I118da434cc379bbdb7bcef4af847216f5124551f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1622105Reviewed-by: Ben Smith <binji@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61718}