fix: add client side check for userslug #8939

public/src/client/register.js

@@ -151,12 +151,12 @@ define('forum/register', [
 		callback = callback || function () {};
 
 		var username_notify = $('#username-notify');
-
-		if (username.length < ajaxify.data.minimumUsernameLength) {
+		var userslug = slugify(username);
+		if (username.length < ajaxify.data.minimumUsernameLength || userslug.length < ajaxify.data.minimumUsernameLength) {
 			showError(username_notify, '[[error:username-too-short]]');
 		} else if (username.length > ajaxify.data.maximumUsernameLength) {
 			showError(username_notify, '[[error:username-too-long]]');
-		} else if (!utils.isUserNameValid(username) || !slugify(username)) {
+		} else if (!utils.isUserNameValid(username) || !userslug) {
 			showError(username_notify, '[[error:invalid-username]]');
 		} else {
 			Promise.allSettled([