[FIX] website_sale: fix traceback with express checkout

It can happen that the payment transaction route is called without the
amount kwargs, the code would crash in that case as we tried to access
it either way.
We moved the code after setting the default amount in the kwargs to
avoid a crash.

closes odoo/odoo#105576

X-original-commit: c124fb3292439a6237f16eff406c0a7d375cab65
Signed-off-by: William Braeckman (wbr) <wbr@odoo.com>

addons/website_sale/controllers/main.py

@@ -1732,9 +1732,6 @@ class PaymentPortal(payment_portal.PaymentPortal):
         if order_sudo.state == "cancel":
             raise ValidationError(_("The order has been canceled."))
 
-        if tools.float_compare(kwargs['amount'], order_sudo.amount_total, precision_rounding=order_sudo.currency_id.rounding):
-            raise ValidationError(_("The cart has been updated. Please refresh the page."))
-
         kwargs.update({
             'reference_prefix': None,  # Allow the reference to be computed based on the order
             'sale_order_id': order_id,  # Include the SO to allow Subscriptions to tokenize the tx
@@ -1742,6 +1739,10 @@ class PaymentPortal(payment_portal.PaymentPortal):
         kwargs.pop('custom_create_values', None)  # Don't allow passing arbitrary create values
         if not kwargs.get('amount'):
             kwargs['amount'] = order_sudo.amount_total
+
+        if tools.float_compare(kwargs['amount'], order_sudo.amount_total, precision_rounding=order_sudo.currency_id.rounding):
+            raise ValidationError(_("The cart has been updated. Please refresh the page."))
+
         tx_sudo = self._create_transaction(
             custom_create_values={'sale_order_ids': [Command.set([order_id])]}, **kwargs,
         )