[FIX] website_sale: existing transaction

If the transaction already exists, the amount total of the transaction must
be updated.
The case occured when:
[1] you put a product A in the cart
[2] click on "Process Checkout" and click "Confirm"
[3] select Adyen or Paypal as payment method
[4] click on "Pay Now"
[5] return in the cart instead of paying your order
[6] add a product B in the cart
[7] click on "Process Checkout" and click "Confirm"
[8] select Adyen or Paypal as payment method
[9] click on "Pay Now"
Now check the transaction payment linked to the order in backend, the total amount of the order is equal
to price A + price B and the total amount of the transaction payment is equal to price A.
This commit solves this problem.
opw:634119

addons/website_sale/controllers/main.py

@@ -699,6 +699,7 @@ class website_sale(http.Controller):
             if tx.state == 'draft':  # button cliked but no more info -> rewrite on tx or create a new one ?
                 tx.write({
                     'acquirer_id': acquirer_id,
+                    'amount': order.amount_total,
                 })
             tx_id = tx.id
         else: