Fix overflow in Windows replacement pg_pread/pg_pwrite.
When calling the Windows file I/O APIs there is an implicit conversion
from size_t to DWORD, which could overflow. Clamp the size at 1GB to
avoid that.
Not a really a live bug as we don't expect anything in PostgreSQL to
call with such large values.
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/
1672202.
1703441340%40sss.pgh.pa.us