Fixx off by one error.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@587 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/hash_classic.c

@@ -176,7 +176,8 @@ hcl_deref(struct objhead *oh)
 	CAST_OBJ_NOTNULL(he, oh->hashpriv, HCL_ENTRY_MAGIC);
 	mtx = he->mtx;
 	AZ(pthread_mutex_lock(&hcl_mutex[mtx]));
-	if (--he->refcnt >= 0) {
+	assert(he->refcnt > 0);
+	if (--he->refcnt > 0) {
 		AZ(pthread_mutex_unlock(&hcl_mutex[mtx]));
 		return (1);
 	}