1. Have a POS with Authorized Employees
2. Startup POS sesssion with an Android phone
3. Click "Select Cashier"

The popup will open partially out of screen,
forcing the user to manually drag it to to center
in order to select a cashier

opw-2476496

closes odoo/odoo#68289

Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>

To reproduce:
0. Login as admin.
1. Install pos_hr.
2. Open a pos session without activating the Authorized employees feature.
3. Make an order as Mitchell admin but **don't** validate, order is just
in the localStorage.
4. Go back to the backend (without closing the browser).
5. Close the session.
6. Edit the pos config and activate authorized employees.
7. Delete the employee record linked to the admin user.
8. Open a new session using the modified pos config.
9. [Crash] Because of missing employee.

Solution:
We just make sure to prevent field access on missing undefined object.

closes odoo/odoo#66319

Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>