uefi-dbx: Fix a critical warning when parsing invalid firmware
uefi-dbx: Fix a critical warning when parsing invalid firmware

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