Make RI on TLS 1.3 alert with ILLEGAL_PARAMETER.

Change-Id: I0e2e4166ad2c57e3192af058f23374f014a2fcf4
Reviewed-on: https://boringssl-review.googlesource.com/14377
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

ssl/t1_lib.c

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index ef4a889..014432e 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -719,6 +719,7 @@
                                     CBS *contents) {
   SSL *const ssl = hs->ssl;
   if (contents != NULL && ssl3_protocol_version(ssl) >= TLS1_3_VERSION) {
+    *out_alert = SSL_AD_ILLEGAL_PARAMETER;
     return 0;
   }