gpg: Stop early when trying to create a primary Elgamal key.

gpg: Stop early when trying to create a primary Elgamal key.

* g10/misc.c (openpgp_pk_test_algo2): Add extra check.
--

The problem is that --key-gen --batch with a parameter file didn't
detect that Elgamal is not capable of signing and so an error was only
triggered at the time the self-signature was created.  See the code
comment for details.

GnuPG-bug-id: 4329
Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit f97dc55ff1b041071bc3cbe98aa761bf77bb7ac8)
(cherry picked from commit f5d3b982e44c5cfc60e9936020102a598b635187)

Gbp-Pq: Topic from-2.2.13
Gbp-Pq: Name gpg-Stop-early-when-trying-to-create-a-primary-Elgamal-ke.patch