Fix error in unsubscriber

- wrong error checking

cmd/hubserver/handler.go

@@ -87,11 +87,19 @@ func (handler *subscriptionHandler) handleUnsubscription(w http.ResponseWriter,
 	topic := r.Form.Get("hub.topic")
 	mode := r.Form.Get("hub.mode")
 
-	if subscribers, err := handler.store.Subscribers(topic); err != nil {
+	subscribers, err := handler.store.Subscribers(topic)
+	if err != nil {
+		return errors.Wrapf(err, "could not get subscribers for %s", topic)
+	}
+
+	found := false
 	for _, subscriber := range subscribers {
 		if subscriber.Callback != callback {
 			continue
 		}
+
+		found = true
+
 		ourChallenge := randStringBytes(12)
 
 		validationURL, err := url.Parse(callback)
@@ -113,12 +121,13 @@ func (handler *subscriptionHandler) handleUnsubscription(w http.ResponseWriter,
 	}
 
 	w.WriteHeader(200)
+	if found {
 		_, err = fmt.Fprintf(w, "Unsubscribed\n")
-		return err
 	} else {
 		http.Error(w, "Hub does not handle subscription for topic", 400)
 	}
-	return nil
+
+	return err
 }
 
 func (handler *subscriptionHandler) handleSubscription(w http.ResponseWriter, r *http.Request) error {