Fixup for prefetching support on macOS
The new code path (commit
6654bb92047) should call FileAccess() first,
like the posix_fadvise() path.
Reported-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/
0827edec-1317-4917-a186-
035eb1e3241d%40eisentraut.org