CC0 fallback license is non sublicensable

CC0 fallback license grant is non sublicensable.
(cf. https://creativecommons.org/publicdomain/zero/1.0/legalcode)
> Affirmer hereby grants to each affected person a royalty-free, non transferable, non sublicensable, non exclusive, irrevocable and unconditional license to exercise Affirmer's Copyright and Related Rights in the Work