trivial: Fix a small leak in dfu_target_parse_sectors()
trivial: Fix a small leak in dfu_target_parse_sectors()

This only happens when it's called multiple times.

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