Keep old method in case of an unsupported protocol

When we're configured with no-ssl3 and we receive an SSL v3 Client Hello, we set
the method to NULL.  We didn't used to do that, and it breaks things.  This is a
regression introduced in 62f45cc.  Keep the old
method since the code is not able to deal with a NULL method at this time.

CVE-2014-3569, PR#3571

Reviewed-by: Emilia Käsper <emilia@openssl.org>
(cherry picked from commit 392fa7a)

ssl/s23_srvr.c

@@ -602,12 +602,14 @@ int ssl23_get_client_hello(SSL *s)
 	if ((type == 2) || (type == 3))
 		{
 		/* we have SSLv3/TLSv1 (type 2: SSL2 style, type 3: SSL3/TLS style) */
-                s->method = ssl23_get_server_method(s->version);
-		if (s->method == NULL)
+		const SSL_METHOD *new_method;
+		new_method = ssl23_get_server_method(s->version);
+		if (new_method == NULL)
 			{
 			SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_UNSUPPORTED_PROTOCOL);
 			goto err;
 			}
+		s->method = new_method;
 
 		if (!ssl_init_wbio_buffer(s,1)) goto err;