Refuse to print GSS_C_NULL_OID, from Rafal Malinowski.

git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@21409 ec53bebd-3082-4978-b11e-865c3cabbd6b

lib/gssapi/mech/gss_oid_to_str.c

@@ -44,6 +44,9 @@ gss_oid_to_str(OM_uint32 *minor_status, gss_OID oid, gss_buffer_t oid_str)
 
     _mg_buffer_zero(oid_str);
 
+    if (oid == GSS_C_NULL_OID)
+	return GSS_S_FAILURE;
+
     ret = der_get_oid (oid->elements, oid->length, &o, &size);
     if (ret) {
 	*minor_status = ret;