... for 32-bit Windows.

When the TLS value is not set the TlsExpansionSlots field of the TEB
struct might be NULL in which case the InternalGetExistingThreadLocal
should return NULL too.

Bug: v8:12653
Change-Id: Ic6c6d8e51e2447551c372720fad0967e9201f3dc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3513835
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79437}