Create a project visible to a portal customer, create a task and attach an attachment. As a portal user, go to the task and download the attachment, the downloaded filename is the numeric identifier of the document instead of the document filename. The `?download=true` force the download of the attachment and correctly set the filename. opw-2008517 closes odoo/odoo#34098 Signed-off-by: Julien Castiaux <Julien00859@users.noreply.github.com>