PKINIT null pointer deref [CVE-2013-1415]

Don't dereference a null pointer when cleaning up.

The KDC plugin for PKINIT can dereference a null pointer when a
malformed packet causes processing to terminate early, leading to
a crash of the KDC process.  An attacker would need to have a valid
PKINIT certificate or have observed a successful PKINIT authentication,
or an unauthenticated attacker could execute the attack if anonymous
PKINIT is enabled.

CVSSv2 vector: AV:N/AC:M/Au:N/C:N/I:N/A:C/E:P/RL:O/RC:C

This is a minimal commit for pullup; style fixes in a followup.
[kaduk@mit.edu: reformat and edit commit message]

(cherry picked from commit c773d3c775e9b2d88bcdff5f8a8ba88d7ec4e8ed)

ticket: 7570
version_fixed: 1.11.1
status: resolved
pkinit_create_td_trusted_certifiers(krb5_context context,
                                    pkinit_plg_crypto_context plg_cryptoctx,
                                    pkinit_req_crypto_context req_cryptoctx,
                                    pkinit_identity_crypto_context id_cryptoctx,
                                    krb5_pa_data ***e_data_out)
{
    krb5_error_code retval = KRB5KRB_ERR_GENERIC;

    retval = pkinit_create_sequence_of_principal_identifiers(context,
                                                             plg_cryptoctx, req_cryptoctx, id_cryptoctx,
                                                             TD_TRUSTED_CERTIFIERS, e_data_out);

    return retval;
}

pkinit_create_td_trusted_certifiers(krb5_context context,
                                    pkinit_plg_crypto_context plg_cryptoctx,
                                    pkinit_req_crypto_context req_cryptoctx,
                                    pkinit_identity_crypto_context id_cryptoctx,
                                    krb5_pa_data ***e_data_out)
{
    krb5_error_code retval = KRB5KRB_ERR_GENERIC;

    retval = pkinit_create_sequence_of_principal_identifiers(context,
                                                             plg_cryptoctx, req_cryptoctx, id_cryptoctx,
                                                             TD_TRUSTED_CERTIFIERS, e_data_out);

    return retval;
}
