fix(x509.c): Fixed regression of openssl x509 -checkend return values

fix(x509.c): Fixed regression of openssl x509 -checkend return values

Fixes #28928

Also adds functionality to -checkend to account for -multi behaviour.
Man page and unit tests updated accordingly.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/29155)