When no SRP identity is found, no error was reported server side

Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1859)

ssl/statem/statem_srvr.c

@@ -1526,6 +1526,9 @@ WORK_STATE tls_post_process_client_hello(SSL *s, WORK_STATE wst)
             if (al != TLS1_AD_UNKNOWN_PSK_IDENTITY)
                 SSLerr(SSL_F_TLS_POST_PROCESS_CLIENT_HELLO,
                        SSL_R_CLIENTHELLO_TLSEXT);
+            else
+                SSLerr(SSL_F_TLS_POST_PROCESS_CLIENT_HELLO,
+                       SSL_R_PSK_IDENTITY_NOT_FOUND);
             goto f_err;
         }
     }