Fix CVE-2014-3470

Check session_cert is not NULL before dereferencing it.
(cherry picked from commit 8011cd56e39a433b1837465259a9bd24a38727fb)

ssl/s3_clnt.c

@@ -2712,6 +2712,13 @@ int ssl3_send_client_key_exchange(SSL *s)
 			int ecdh_clnt_cert = 0;
 			int field_size = 0;
 
+			if (s->session->sess_cert == NULL) 
+				{
+				ssl3_send_alert(s,SSL3_AL_FATAL,SSL_AD_UNEXPECTED_MESSAGE);
+				SSLerr(SSL_F_SSL3_SEND_CLIENT_KEY_EXCHANGE,SSL_R_UNEXPECTED_MESSAGE);
+				goto err;
+				}
+
 			/* Did we send out the client's
 			 * ECDH share for use in premaster
 			 * computation as part of client certificate?