A single ClusterFuzz report flushed out two minor issues in the
bit fiddling routines.

Bug: chromium:1227752,v8:11515
Change-Id: I16ab914b7c3859f55aa141ced371dd80171d0cb5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3017809Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75678}