No device comes off the shelf with OpenWRT. If you're the type of person that's aware of OpenWRT and then install it, it's not that far of a stretch to think you'd also be the type to know to check the password.
GL-inet devices come off the shelf with OpenWRT. They don't have a blank password. Every single one ships with 'goodlife' as the default password, as printed on the label on the back.