[FIX] point_of_sale: cash balance

- Go to POS application
- Click on the 3 dots of the session to open configuration
- Remove the "Cash" payment method and just keep "Bank"
- Open the session, proceed to a sell and close it.
- Try to open the session either clicking on "Close" on the kanban card

`CacheMiss` error.

opw-2116470

closes odoo/odoo#39570

X-original-commit: 62cb92644de3cfa6e7864583d1efcaf5821f05e4
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/point_of_sale/models/pos_session.py

@@ -112,6 +112,10 @@ class PosSession(models.Model):
                 )
                 session.cash_register_balance_end = session.cash_register_balance_start + session.cash_register_total_entry_encoding
                 session.cash_register_difference = session.cash_register_balance_end_real - session.cash_register_balance_end
+            else:
+                session.cash_register_total_entry_encoding = 0.0
+                session.cash_register_balance_end = 0.0
+                session.cash_register_difference = 0.0
 
     @api.depends('order_ids.payment_ids.amount')
     def _compute_total_payments_amount(self):