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
free_cred_info(krb5_context context,
               pkinit_identity_crypto_context id_cryptoctx,
               struct _pkinit_cred_info *cred)
{
    if (cred != NULL) {
        if (cred->cert != NULL)
            X509_free(cred->cert);
        if (cred->key != NULL)
            EVP_PKEY_free(cred->key);
#ifndef WITHOUT_PKCS11
        free(cred->cert_id);
#endif
        free(cred->name);
        free(cred);
    }
}

free_cred_info(krb5_context context,
               pkinit_identity_crypto_context id_cryptoctx,
               struct _pkinit_cred_info *cred)
{
    if (cred != NULL) {
        if (cred->cert != NULL)
            X509_free(cred->cert);
        if (cred->key != NULL)
            EVP_PKEY_free(cred->key);
#ifndef WITHOUT_PKCS11
        free(cred->cert_id);
#endif
        free(cred->name);
        free(cred);
    }
}
