Fix kadm5/gssrpc XDR double free [CVE-2014-9421]

Fix kadm5/gssrpc XDR double free [CVE-2014-9421]

[MITKRB5-SA-2015-001] In auth_gssapi_unwrap_data(), do not free
partial deserialization results upon failure to deserialize.  This
responsibility belongs to the callers, svctcp_getargs() and
svcudp_getargs(); doing it in the unwrap function results in freeing
the results twice.

In xdr_krb5_tl_data() and xdr_krb5_principal(), null out the pointers
we are freeing, as other XDR functions such as xdr_bytes() and
xdr_string().

(cherry picked from commit a197e92349a4aa2141b5dff12e9dd44c2a2166e3)

ticket: 8068 (new)
version_fixed: 1.12.3
status: resolved