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

this information is no longer available.

Fixes #1228

bin/varnishd/cache_vrt_var.c

@@ -536,6 +536,12 @@ unsigned
 VRT_r_req_backend_healthy(const struct sess *sp)
 {
 	CHECK_OBJ_NOTNULL(sp, SESS_MAGIC);
+       /*
+        * XXX: Not optimal, but we do not have a backend in vcl_deliver
+        * XXX: and we have to return something.
+        */
+       if (sp->director == NULL)
+	       return (0);
 	CHECK_OBJ_NOTNULL(sp->director, DIRECTOR_MAGIC);
 	return (VDI_Healthy(sp->director, sp));
 }

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