[FIX] l10n_it_withholding_tax: amount_net_pay_residual can't be negative

This happens in case of refund reconciliation

l10n_it_withholding_tax/models/account.py

@@ -322,6 +322,8 @@ def _compute_amount_withholding_tax(self):
             for line in reconciled_amls:
                 if not line.withholding_tax_generated_by_move_id:
                     amount_net_pay_residual -= line.debit or line.credit
+            if amount_net_pay_residual < 0:
+                amount_net_pay_residual = 0
             invoice.amount_net_pay_residual = float_round(
                 amount_net_pay_residual, dp_obj.precision_get("Account")
             )