[FIX] website_form: Allow to post a message with attachments

Coming from the sudo() modification. The mail.message is created in sudo,
but the user is still the public user, who doesn't have a email address,
leading to an raised error.

addons/website_form/controllers/main.py

@@ -8,7 +8,7 @@ import pytz
 from datetime import datetime
 from psycopg2 import IntegrityError
 
-from odoo import http
+from odoo import http, SUPERUSER_ID
 from odoo.http import request
 from odoo.tools import DEFAULT_SERVER_DATE_FORMAT, DEFAULT_SERVER_DATETIME_FORMAT
 from odoo.tools.translate import _
@@ -236,7 +236,7 @@ class WebsiteForm(http.Controller):
                     'res_id': id_record,
                     'attachment_ids': [(6, 0, orphan_attachment_ids)],
                 }
-                mail_id = request.env['mail.message'].sudo().create(values)
+                mail_id = request.env['mail.message'].with_user(SUPERUSER_ID).create(values)
         else:
             # If the model is mail.mail then we have no other choice but to
             # attach the custom binary field files on the attachment_ids field.