fix webfinger responses according to the specs (#2397)

* webfinger query with no resource should get 400

* check valid webfinger query

* test webfinger query

... without acct: or with wrong server

* add test for invalid user query from webfinger

* reorder the tests to decouple from state

cleanup

activitypub/controllers/webfinger.go

@@ -30,6 +30,7 @@ func WebfingerHandler(w http.ResponseWriter, r *http.Request) {
 
 	userComponents := strings.Split(account, "@")
 	if len(userComponents) < 2 {
+		w.WriteHeader(http.StatusBadRequest)
 		return
 	}
 	host := userComponents[1]
@@ -46,7 +47,7 @@ func WebfingerHandler(w http.ResponseWriter, r *http.Request) {
 	// should be rejected.
 	instanceHostString := data.GetServerURL()
 	if instanceHostString == "" {
-		w.WriteHeader(http.StatusNotImplemented)
+		w.WriteHeader(http.StatusNotFound)
 		return
 	}