[FIX] account: send several invoices => state sent

When we print or post_message of an invoice it is set as sent.

But when we multiprint, we do not use each invoice post_message but
create directly mail.mail then send them in batch.

Thus the invoices are not set as "Sent".

With this change we make a special case.

opw-1910937
closes #28852

addons/account/wizard/account_invoice_send.py

@@ -49,6 +49,8 @@ def onchange_template_id(self):
     def _send_email(self):
         if self.is_email:
             self.composer_id.send_mail()
+            if self.env.context.get('mark_invoice_as_sent'):
+                self.mapped('invoice_ids').write({'sent': True})
 
     @api.multi
     def _print_document(self):