Recommended by clang-tidy's modernize-use-nullptr.

Bug: v8:10488
Change-Id: I03a6af87f281c52edd01f3ad91f9ec6e28d398d0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2233985Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68302}