trivial: Return with an error if the device GType is unclear
trivial: Return with an error if the device GType is unclear

Returning TRUE means this is really hard to debug...

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