check-meta: fix 'hasNoMaintainers' (#412184)

  hasUnfreeLicense = attrs: hasLicense attrs && isUnfree attrs.meta.license;

  hasNoMaintainers =

    # To get usable output, we want to avoid flagging "internal" derivations.

    # Because we do not have a way to reliably decide between internal or

    # external derivation, some heuristics are required to decide.

    #

    # If `outputHash` is defined, the derivation is a FOD, such as the output of a fetcher.

    # If `description` is not defined, the derivation is probably not a package.

    # Simply checking whether `meta` is defined is insufficient,

    # as some fetchers and trivial builders do define meta.

    attrs:

    (attrs ? meta.maintainers && (length attrs.meta.maintainers) == 0)

    && (attrs ? meta.teams && (length attrs.meta.teams) == 0);

    (!attrs ? outputHash)

    && (attrs ? meta.description)

    && (attrs.meta.maintainers or [ ] == [ ])

    && (attrs.meta.teams or [ ] == [ ]);

  isMarkedBroken = attrs: attrs.meta.broken or false;