MINOR: cli: can't connect to the target CLI

Return an error and quit if the CLI proxy is not able to connect to a
target.
diff --git a/src/cli.c b/src/cli.c
index 999e4c0..32eaf46 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -1926,6 +1926,11 @@
 	struct proxy *fe = strm_fe(s);
 	struct proxy *be = s->be;
 
+	if (rep->flags & CF_READ_ERROR) {
+		pcli_reply_and_close(s, "Can't connect to the target CLI!\n");
+		s->res.analysers &= ~AN_RES_WAIT_CLI;
+		return 0;
+	}
 	rep->flags |= CF_READ_DONTWAIT; /* try to get back here ASAP */
 	rep->flags |= CF_NEVER_WAIT;