core,w32: Fix new w32-util functions

* src/w32-util.c (_gpgme_access): Respect mode parameter.
(_gpgme_create_process_utf8): Convert startupinfo, too.

This both did not show up in testing as we only use
mode F_OK and STARTUPINFOA is basically the same as
STARTUPINFOW.

Fixes commit: a82e3a0ae57a48ba173e282a050680751006c074

• GnuPG-Bug-Id: T4453