From 43a63019f5bdc627170212ec5ed8c1333ad4727b Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Mon, 13 Jan 2020 19:02:55 +0000
Subject: [PATCH] Fix ldisc_send() assertion in terminal answerback.

A user reports that if the ^E answerback string is configured to be
empty, then causing the answerback to be sent fails the assertion in
ldisc_send introduced in commit c269dd013.

I thought I'd caught all of the remaining cases of this in commit
4634cd47f, but apparently not.
---
 terminal.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/terminal.c b/terminal.c
index ad54463b..db397e9c 100644
--- a/terminal.c
+++ b/terminal.c
@@ -3406,7 +3406,8 @@ static void term_out(Terminal *term)
                     strbuf *buf = term_input_data_from_charset(
                         term, DEFAULT_CODEPAGE,
                         term->answerback, term->answerbacklen);
-                    ldisc_send(term->ldisc, buf->s, buf->len, false);
+                    if (buf->len)
+                        ldisc_send(term->ldisc, buf->s, buf->len, false);
                     strbuf_free(buf);
                 }
                 break;