nix ls-nar: allow reading from FIFOs
nix ls-nar: allow reading from FIFOs

fixes #2528

dtzWill/nix,ehmry/nix,vcunat/nix,NixOS/nix,ehmry/nix,zimbatm/nix,rycee/nix,rycee/nix,NixOS/nix,ehmry/nix,pikajude/nix,dtzWill/nix,dtzWill/nix,pikajude/nix,rycee/nix,vcunat/nix,zimbatm/nix,dtzWill/nix,pikajude/nix,ehmry/nix,NixOS/nix,zimbatm/nix,rycee/nix,NixOS/nix,NixOS/nix,ehmry/nix,zimbatm/nix,vcunat/nix,rycee/nix,dtzWill/nix,ehmry/nix,vcunat/nix