The fast-path in the `ArrayPrototypeLastIndexOf` torque implementation
didn't check that the `fromIndex` is within the bounds of the JSArray
_AFTER_ the call to ToInteger, which can have arbitrary side-effects,
i.e. it can change the length of the array.

R=yangguo@chromium.org

Bug: chromium:898785
Change-Id: I7ef84143ec8c33148f6e9d451bd52769d5074fb4
Reviewed-on: https://chromium-review.googlesource.com/c/1314329Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57204}