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

Bug: v8:10488
Change-Id: I7cf26f7bda69b9b1a6bdabe274399b494f6d49ed
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2211155Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67979}