dirmngr: Minor fix for baseDN fallback.

* dirmngr/ks-engine-ldap.c (my_ldap_connect): Avoid passing data
behind the EOS.
(interrogate_ldap_dn): Stylistic change.

This also updates the my_ldap_connect description.

(cherry picked from commit 11aa5a93a754fe978d0f35d7fbeb4767b6b6df05)

• GnuPG-bug-id: T6047