This prevents some code (in controllers) to retrieve an attachment for a field that is not stored, as the code only relies on `field.attachment`. This also makes the field definition more consistent. closes odoo/odoo#57980 X-original-commit: 7325c3f8c538a8b8c0435963cdda3ced6fe4b324 Signed-off-by: Raphael Collet (rco) <rco@openerp.com>