png images not shown on ir.attachment kanban Attachment that use db_datas have no checksum by default, which is used to compute the stream's http ETag. Skip updating the ETag when it is missing and determine freshness using the Last-Modified header instead. closes odoo/odoo#139498 X-original-commit: 2d43bbae72fddf17e7d9045e90dbc070b2f57a19 Signed-off-by: Julien Castiaux (juc) <juc@odoo.com>