HeapAllocator didn't fall back to old space allocation when the
heap had no map space.

Bug: v8:12578, chromium:1313119
Change-Id: Ic02334f42f9fb80a8a9dcf99a94a7ac16da24053
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3570423Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79776}