[FIX] account_facturx: retrieve attachments in the right way to create an invoice

Before that, we relied on the fact the call to super() assigned the attachment_ids field, which was wrong outside mail.compose.message. Hence, we fix that by directly browsing the attachment.

closes odoo/odoo#36552

Signed-off-by: Laurent Smet <smetl@users.noreply.github.com>

addons/account_facturx/models/account_move.py

@@ -222,7 +222,7 @@ class AccountMove(models.Model):
         res = super(AccountMove, self).message_post(**kwargs)
 
         if 'no_new_invoice' not in self.env.context and len(self) == 1 and self.state == 'draft':
-            for attachment in res.attachment_ids:
+            for attachment in self.env['ir.attachment'].browse(kwargs.get('attachment_ids', [])):
                 self._create_invoice_from_attachment(attachment)
         return res