[FIX] (account, sale)_payment: fix s2s on not existing document

Returned error was not correct as just browsing an ID that
does not exist is not sufficient. We should use exists.

addons/account_payment/controllers/payment.py

@@ -64,7 +64,7 @@ class PaymentPortal(http.Controller):
         if access_token:
             params['access_token'] = access_token
 
-        invoice_sudo = request.env['account.invoice'].sudo().browse(invoice_id)
+        invoice_sudo = request.env['account.invoice'].sudo().browse(invoice_id).exists()
         if not invoice_sudo:
             params['error'] = 'pay_invoice_invalid_doc'
             return request.redirect(_build_url_w_params(error_url, params))

addons/sale_payment/controllers/payment.py

@@ -64,7 +64,7 @@ class PaymentPortal(http.Controller):
         if access_token:
             params['access_token'] = access_token
 
-        order_sudo = request.env['sale.order'].sudo().browse(order_id)
+        order_sudo = request.env['sale.order'].sudo().browse(order_id).exists()
         if not order_sudo:
             params['error'] = 'pay_sale_invalid_doc'
             return request.redirect(_build_url_w_params(error_url, params))