argparser: avoid endless loop due to a conf file read error.
* src/argparse.c (struct _gpgrt_argparse_internal_s): Add forceeof flag. (initialize): Clear. (_gpgrt_argparse): Clear. (_gpgrt_argparse): Act upon.
Reported test case:
$ mkdir /etc/gnupg/gpg.conf $ gpg --version
All other ways to force a read error will also exhibit the bug.
- Debian-bug-id: #1068594