[FIX] account_payment: properly compute destination account without p…

…artner

When the `partner_id` is not set (it is not required at the model
level), we can still compute the default destination account based on
the company chart of account configuration.

This is necessary to allow creating "customer" or "supplier" payments without
selecting a specific partner.

addons/account/models/account_payment.py

@@ -361,6 +361,12 @@ def _compute_destination_account_id(self):
                 self.destination_account_id = self.partner_id.property_account_receivable_id.id
             else:
                 self.destination_account_id = self.partner_id.property_account_payable_id.id
+        elif self.partner_type == 'customer':
+            default_account = self.env['ir.property'].get('property_account_receivable_id', 'res.partner')
+            self.destination_account_id = default_account.id
+        elif self.partner_type == 'supplier':
+            default_account = self.env['ir.property'].get('property_account_payable_id', 'res.partner')
+            self.destination_account_id = default_account.id
 
     @api.onchange('partner_type')
     def _onchange_partner_type(self):