[FIX] account: Wrong payment amount in multi-currency

Steps to reproduce:

- activate the EUR currency

- set a currency rate 1 USD = 1.2 EUR

- create a Bank journal in EUR with a EUR account

- create a Vendor Bill in EUR for 1200 EUR in total

- go in the Vendor Bill list view (Accounting > Purchase > Vendor Bills)

- select the created Vendor Bill

- click "Register Payment" in the action menu

- select the EUR Bank journal you created

Bug:

The payment amount is 1000 EUR instead of 1200 EUR.

opw:1870351

addons/account/models/account_payment.py

@@ -113,18 +113,26 @@ class account_register_payments(models.TransientModel):
 
     @api.model
     def _compute_payment_amount(self, invoice_ids):
-        payment_currency = self.currency_id or self.journal_id.currency_id or self.journal_id.company_id.currency_id
+        payment_currency = self.currency_id or self.journal_id.currency_id or self.journal_id.company_id.currency_id or invoice_ids and invoice_ids[0].currency_id
 
         total = 0
         for inv in invoice_ids:
             if inv.currency_id == payment_currency:
-                total += MAP_INVOICE_TYPE_PAYMENT_SIGN[inv.type] * inv.residual_company_signed
+                total += MAP_INVOICE_TYPE_PAYMENT_SIGN[inv.type] * inv.residual_signed
             else:
                 amount_residual = inv.company_currency_id.with_context(date=self.payment_date).compute(
                     inv.residual_company_signed, payment_currency)
                 total += MAP_INVOICE_TYPE_PAYMENT_SIGN[inv.type] * amount_residual
         return total
 
+    @api.onchange('journal_id')
+    def _onchange_journal(self):
+        res = super(account_register_payments, self)._onchange_journal()
+        active_ids = self._context.get('active_ids')
+        invoices = self.env['account.invoice'].browse(active_ids)
+        self.amount = abs(self._compute_payment_amount(invoices))
+        return res
+
     @api.model
     def default_get(self, fields):
         rec = super(account_register_payments, self).default_get(fields)