Fix underflow in allocation timeout which is used by fuzzers to trigger
garabge collection.

Bug: chromium:1337646
Change-Id: Iffa70497c2945a26242e9e67820197bd5e61f04c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3711758
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81246}