[FIX] website_event: traceback on register button

How to reproduce the bug
========================
​1.Open the register page of an event
2.Do not pick any ticket
3.Click Register
=> an traceback is raised

Technical
=========
'?.length > 0' statement was checking the length of the array instead of the
values of the array.

This issue comes after this https://github.com/odoo/odoo/pull/120437

After this commit:
==================
Now the traceback will not raise.

Task-3329432

closes odoo/odoo#126352

X-original-commit: 1c47606cf1cd56c4d0980c7419c508e37c90f58f
Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>

addons/website_event/static/src/js/website_event.js

@@ -44,8 +44,10 @@ var EventRegistrationForm = Widget.extend({
         $('#registration_form select').each(function () {
             post[$(this).attr('name')] = $(this).val();
         });
-        var tickets_ordered = Object.values(post).map((value) => parseInt(value))?.length > 0;
-        if (!tickets_ordered) {
+
+        // "post" looks like: { nb_register-9: "2", nb_register-10: "0" }
+        const noTicketsOrdered = Object.values(post).map((value) => parseInt(value)).every(value => value === 0);
+        if (noTicketsOrdered) {
             $('<div class="alert alert-info"/>')
                 .text(_t('Please select at least one ticket.'))
                 .insertAfter('#registration_form table');