gpgconf: No ENOENT warning with --change-options et al.
* tools/gpgconf-comp.c (retrieve_options_from_program): Check ERRNO before printing a warning.
It is common that a conf files does not exist - thus we should not
print a warning.
BTW: The error messages in gpgconf should be reworked to match those
of the other components.
- GnuPG-bug-id: T2944
- Signed-off-by: Werner Koch <wk@gnupg.org>