trivial: Fix a potential crash spotted with clang
trivial: Fix a potential crash spotted with clang

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