We depend on the xdr decoder to set this pointer, but if we error out
before we decode this piece it could be left NULL.

I think this is probably tough to hit without a buggy gss-proxy.
Reported-by: Andi Kleen <andi@firstfloor.org>
Cc: Simo Sorce <simo@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>