Fix a Telegram-related bug

I removed my favorite comment:

// Problems is something we put blankets on.

auth/web.go

@@ -170,8 +170,9 @@ func handlerTelegramLogin(w http.ResponseWriter, rq *http.Request) {
 			false,
 		)
 	)
+	// If registering a user via Telegram failed, because a Telegram user with this name
+	// has already registered, then everything is actually ok!
 	if user.HasUsername(username) && user.ByName(username).Source == "telegram" {
-		// Problems is something we put blankets on.
 		err = nil
 	}
 

user/net.go

@@ -59,7 +59,7 @@ func Register(username, password, group, source string, force bool) error {
 		return fmt.Errorf("username ‘%s’ is already taken", username)
 	case !force && cfg.RegistrationLimit > 0 && Count() >= cfg.RegistrationLimit:
 		return fmt.Errorf("reached the limit of registered users (%d)", cfg.RegistrationLimit)
-	case password == "":
+	case password == "" && source != "telegram":
 		return fmt.Errorf("password must not be empty")
 	}