[FIX] account_payment_pro: filter empty currency_id in _onchange_amount_update_exact

[feg-adhoc]

Summary

When a user without full permissions opens the payment wizard from an invoice, the currency_id field arrives as an empty recordset in the onchange context. Calling .is_zero() on it triggers ensure_one() → ValueError: Expected singleton: res.currency().

Fix: use self.filtered("currency_id") to skip records with no currency before entering the loop, consistent with how _compute_amount already handles this case.

Changes

• account_payment_pro/models/account_payment.py: _onchange_amount_update_exact — iterate over self.filtered("currency_id") instead of self.

Test plan

• Open an invoice and click "Register Payment" with a user that has restricted permissions.
• Verify the payment wizard opens without RPC error.
• Change the amount and confirm the amount_exact field updates correctly.

[roboadhoc]

[Copilot]

Pull request overview

Este PR busca evitar un error en el wizard de pagos cuando currency_id llega vacío en el contexto de onchange (p. ej. con usuarios restringidos), lo que provocaba un ensure_one() al llamar currency_id.is_zero().

Changes:

• Ajusta _onchange_amount_update_exact para no ejecutar .is_zero() cuando currency_id está vacío.