Ignore missing reason in probe responses

Fixes #2069

bin/varnishd/cache_backend_poll.c

@@ -226,7 +226,7 @@ vbp_poke(struct vbp_target *vt)
 
 	i = sscanf(vt->resp_buf, "HTTP/%*f %u %s", &resp, buf);
 
-	if (i == 2 && resp == vt->probe.exp_status)
+	if (i >= 1 && resp == vt->probe.exp_status)
 		vt->happy |= 1;
 }
 

bin/varnishtest/tests/r02069.vtc

+varnishtest "Probe response without a reason"
+
+server s1 -repeat 20 {
+	rxreq
+	send "HTTP/1.1 200\r\n\r\n"
+} -start
+
+varnish v1 -vcl {
+	backend s1 {
+		.host = "${s1_addr}";
+		.port = "${s1_port}";
+		.probe = {
+			.initial = 0;
+			.window = 5;
+			.threshold = 5;
+			.interval = 100ms;
+		}
+	}
+
+	sub vcl_recv {
+		if (req.backend.healthy) {
+			error 200 "Backend healthy";
+		}
+		else {
+			error 500 "Backend sick";
+		}
+	}
+} -start
+
+delay 1
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+} -run