Return false if req.backend.health is accessed in vcl_deliver{} where

this information is no longer available.

Fixes #1228

bin/varnishd/cache/cache_vrt_var.c

@@ -555,6 +555,12 @@ unsigned
 VRT_r_req_backend_healthy(const struct req *req)
 {
 	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);
+	/*
+	 * XXX: Not optimal, but we do not have a backend in vcl_deliver
+	 * XXX: and we have to return something.
+	 */
+	if (req->director == NULL)
+		return (0);
 	CHECK_OBJ_NOTNULL(req->director, DIRECTOR_MAGIC);
 	return (VDI_Healthy(req->director, req));
 }

bin/varnishtest/tests/r01228.vcl

+varnishtest "req.backend.healthy in vcl_deliver"
+
+server s1 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl+backend {
+	sub vcl_deliver {
+	    set resp.http.x-foo = req.backend.healthy;
+	}
+} -start
+
+client c1 {
+	txreq
+	rxresp
+	expect resp.status == 200
+} -run