[FIX] sale: make payment when journal type is not sale

This traceback arises when a user tries to make a payment on the website.

To reproduce this issue:

1) Install 'website_sale'
2) open invoicing/configuration/journals
3) Change the journal type if it is 'sales'
4) Install and enable 'Wire Transfer' payment provider in
   invocing/configuration/Payment Providers
5) Now open 'website/shop' add any product to cart and proceed to checkout
6) Make a payment with 'Wire Transfer'

Error: 'ValueError Expected singleton: account.journal()'

On '_compute_sale_order_reference' method, 'invoice_journal' variable
is getting values with the reference of 'type=sale'.
See:-
https://github.com/odoo/odoo/blob/ebc4ed6c4fb11b01be28cf417b27de83d5361cef/addons/sale/models/payment_transaction.py#L20-L30

Because of user changed the type of journal, 'invoice_journal'
value will be empty recordset and it is referenced to call
'_process_reference_for_sale_order' method.

In '_process_reference_for_sale_order' method ensure_one() is used,
which leads to above traceback.

sentry-4392496618

closes odoo/odoo#134083

X-original-commit: c880a295d0f7feff48b08fd00723a41b8d564d2d
Signed-off-by: Olivier Colson (oco) <oco@odoo.com>
Signed-off-by: Altaf Shaik (alsh) <alsh@odoo.com>

addons/sale/models/payment_transaction.py

@@ -24,7 +24,8 @@ class PaymentTransaction(models.Model):
             order_reference = '%s/%s' % ('CUST', str(identification_number % 97).rjust(2, '0'))
 
         invoice_journal = self.env['account.journal'].search([('type', '=', 'sale'), ('company_id', '=', self.env.company.id)], limit=1)
-        order_reference = invoice_journal._process_reference_for_sale_order(order_reference)
+        if invoice_journal:
+            order_reference = invoice_journal._process_reference_for_sale_order(order_reference)
 
         return order_reference