Fix configuring provider certificate algs via config file

Fix configuring provider certificate algs via config file

A crash could occur when attempting to configure a certificate via a
config file, where the algorithm for the certificate key was added
dynamically via a provider.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26663)