Merge r3799: Don't rush waiting sessions always

Don't try to rush waiting sessions of refcount is zero, there cannot be
any (they would hold a reference).

Should be merged to 2.0.3



git-svn-id: http://www.varnish-cache.org/svn/branches/2.0@3817 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_hash.c

@@ -435,7 +435,8 @@ HSH_Deref(struct object **oo)
 	assert(o->refcnt > 0);
 	r = --o->refcnt;
 	if (oh != NULL)
-		hsh_rush(oh);
+		else
+			hsh_rush(oh);
 	if (oh != NULL) {
 		if (!r)
 			VTAILQ_REMOVE(&oh->objects, o, list);