maintainers: add targeted fix for missing `pkgs/by-name/.../package.nix` files (#341041)

# nix-build build.nix --argstr maintainer <yourname> --argstr system aarch64-linux

let

  pkgs = import ./../../default.nix (removeAttrs args [ "maintainer" ]);

  # This avoids a common situation for maintainers, where due to Git's behavior of not tracking

  # directories, they have an empty directory somewhere in `pkgs/by-name`. Because that directory

  # exists, `pkgs/top-level/by-name-overlay.nix` picks it up and attempts to read `package.nix` out

  # of it... which doesn't exist, since it's empty.

  #

  # We don't want to run the code below on every instantiation of `nixpkgs`, as the `pkgs/by-name`

  # eval machinery is quite performance sensitive. So we use the internals of the `by-name` overlay

  # to implement our own way to avoid an evaluation failure for this script.

  #

  # See <https://github.com/NixOS/nixpkgs/issues/338227> for more motivation for this code block.

  overlay = self: super: {

    _internalCallByNamePackageFile =

      file: if builtins.pathExists file then super._internalCallByNamePackageFile file else null;

  };

  nixpkgsArgs = removeAttrs args [ "maintainer" "overlays" ] // {

    overlays = args.overlays or [] ++ [ overlay ];

  };

  pkgs = import ./../../default.nix nixpkgsArgs;

  maintainer_ = pkgs.lib.maintainers.${maintainer};

  packagesWith = cond: return: set:

    (pkgs.lib.flatten