Drive-by: simplifications and avoid a repeated concurrent read.

Bug: v8:7790,v8:12157
Change-Id: I460c44853a78bcd9a1427e62a92994ff8602dbed
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3133148
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76640}