thunderbolt: validation: don't print empty strings
thunderbolt: validation: don't print empty strings

Before: "Given location is outside of the given FW ((null))"

hughsie/fwupd,vathpela/fwupd,superm1/fwupd,superm1/fwupd,fwupd/fwupd,fwupd/fwupd,superm1/fwupd,hughsie/fwupd,vathpela/fwupd,hughsie/fwupd,hughsie/fwupd,vathpela/fwupd,fwupd/fwupd,vathpela/fwupd,fwupd/fwupd