kbx: Use es_sysopen_nc instead of es_fdopen_nc.

* kbx/kbxserver.c (prepare_outstream): Use es_sysopen_nc
and avoid the use of translate_sys2libc_fd.

On Windows, it's better directly use the system HANDLE.

• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>