SimulateFullSpace starts with no LAB, iterates over pages and allocates
all free space on each page. After the first page, the LAB is empty but
is no longer null.

Bug: v8:12612
Change-Id: I2c00b9ba68fdd5f60eda086ea940cb6e211a986e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3891294
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83186}