Check plugins set error on failure
Check plugins set error on failure

Don't explode in a ball of flames if the plugin forgets to set the error.
This at least gives us a journal warning when a plugin goes crazy.

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