Calls to `VirtualFree` that pass `MEM_RELEASE` must specify a size of 0
as the OS will be freeing the original range for the given base address.
The calls to free `MMap` memory on Windows were silently failing because
of an incorrect assertion (on Windows, `VirtualFree` returns non-zero
for success).
This was caught via AppVerifier while investigating a heap overrun issue
on a different PR.
6750605a61