Ipa: freeipa: null pointer dereference in `ipa-enrollment` extended operation (`join_oid`) via missing request value

A flaw was found in the `ipa-enrollment` SLAPI plugin. A remote authenticated client can exploit a null pointer dereference vulnerability by sending a malformed Lightweight Directory Access Protocol (LDAP) extended operation. By omitting the request value for the `JOIN_OID` in the `ipa-enrollment` extended operation, an attacker can trigger a server crash, potentially causing a denial of service.