Send an alert if we fail to pick a signature algorithm.

Change-Id: Id7f5ef9932c4c491bd15085e3c604ebfcf259b7c
Reviewed-on: https://boringssl-review.googlesource.com/29665
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/ssl/handshake_client.cc b/ssl/handshake_client.cc
index a99f87e..de5d8e9 100644
--- a/ssl/handshake_client.cc
+++ b/ssl/handshake_client.cc
@@ -1350,6 +1350,7 @@
 
   uint16_t signature_algorithm;
   if (!tls1_choose_signature_algorithm(hs, &signature_algorithm)) {
+    ssl_send_alert(ssl, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
     return ssl_hs_error;
   }
   if (ssl_protocol_version(ssl) >= TLS1_2_VERSION) {