trivial: Show when there are no subsystem devices
trivial: Show when there are no subsystem devices

If we asked for a subsystem, it's nice to know there are not actually any of the
supported devices.

hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd