[FIX] point_of_sale: prevent traceback while open session with the portal user

when the user allows multi employee per session and the portal user tries to
access the pos with the URL /pos/ui?config_id=1 then the error will be generated.

steps to reproduce:

- Installed point_of_sale module.
- In Configuration > Point of Sale > activate Multi Employees per Session option
  and save it.
- In another window, do log in as a demo user and start the pos session.
- From the Admin user, make Marc Demo as a portal user.
- Then refresh the demo user session.
- Traceback will be generated

Applying these changes will resolve this issue.

sentry - 3958755602

closes odoo/odoo#124662

X-original-commit: 49447781b95f18a87491e47c19e4e8a6167ccf1d
Signed-off-by: Robin Heinz (rhe) <rhe@odoo.com>

addons/point_of_sale/controllers/main.py

@@ -28,6 +28,9 @@ class PosController(PortalAccount):
         :type config_id: str.
         :returns: object -- The rendered pos session.
         """
+        is_internal_user = request.env.user.has_group('base.group_user')
+        if not is_internal_user:
+            return request.not_found()
         domain = [
                 ('state', 'in', ['opening_control', 'opened']),
                 ('user_id', '=', request.session.uid),