If huft_build() fails, gzio->tl or gzio->td could contain pointers that are no longer valid. Zero them out. This prevents a double free when grub_gzio_close() comes through and attempts to free them again. Signed-off-by: Daniel Axtens <dja@axtens.net> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>