[FIX] l10n_ar_account_withholding: render report

Now report render on mail_compose_message not fails when try
send the payment's mail

closes #709

Signed-off-by: Katherine Zaoral <kz@adhoc.com.ar>

l10n_ar_account_withholding/models/mail_compose_message.py

@@ -19,7 +19,7 @@ def _onchange_template_id(self, template_id, composition_mode, model, res_id):
             attachment_ids = []
             for payment in payment_group.payment_ids.filtered(lambda p: p.payment_method_code == 'withholding'):
                 report_name = safe_eval.safe_eval(report.print_report_name, {'object': payment})
-                result, format = report._render(payment.ids)
+                result, format = self.env['ir.actions.report']._render(report.report_name, payment.ids)
                 file = base64.b64encode(result)
                 data_attach = {
                     'name': report_name,