wacom-usb: Fix a buffer-overread spotted by AddressSanitizer
wacom-usb: Fix a buffer-overread spotted by AddressSanitizer

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