This CL changes MaybeLocal::ToLocal documentation to assign |out|
with nullptr when the MaybeLocal is empty to be consistent with
the behavior.

Bug: v8:12845
Change-Id: I8145d6604c51b79f137b686b3e9b4f328534e0a8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3616432
Commit-Queue: 王澳 <wangao.james@bytedance.com>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80329}