[FIX] point_of_sale: closing session without cash

The closing session popup input for bank payment methods throws an error when no cash payment method is configured.

Steps to reproduce:
 - Configure a shop without any cash payment method and with at least one bank payment method
 - Open a session for that shop
 - Click on the button to display the closing session popup
 - In the popup, change the amount of the bank payment method

An error is thrown.

The fix simply consists in correctly checking if there is a cash payment method.

closes odoo/odoo#132473

Task-id: 3468828
Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>