nixos/gollum: make preStart conditional (#374981)

      after = [ "network.target" ];

      wantedBy = [ "multi-user.target" ];

      path = [ pkgs.git ];

      preStart = ''

        # This is safe to be run on an existing repo

        git init ${cfg.stateDir}

        # Check if it's a bare repository.

        IS_BARE=$(git -C "${cfg.stateDir}" rev-parse --is-bare-repository 2>/dev/null || echo "false")

        if [ "$IS_BARE" = "true" ]; then

          echo "Directory is a bare repository. Skipping initialization."

        else

          echo "Directory is not a bare repository. Initializing..."

          git init "${cfg.stateDir}"

        fi

      '';

      serviceConfig = {