The test was supposed to manipulate the serialized bytes to make them
invalid, but the value at the manipulated position was already 0, hence
the bytes stayed valid. This went unnoticed before
https://crrev.com/c/2010786, since there was a fallback anyway to
re-compile the module if deserialization fails.

This CL fixes this by using the right offset, and checking that the
value there is not already zero.

R=thibaudm@chromium.org

Change-Id: Ie0eaf2c8ee9e8c4c477f717f3d8aed8564b3adbf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2007493
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65898}