pihole-ftl: Fix log deleter service creating an empty database

        script =

          let

            days = toString cfg.queryLogDeleter.age;

            database = "${cfg.stateDirectory}/pihole-FTL.db";

            database = cfg.settings.files.database;

          in

          ''

            set -euo pipefail

            # Avoid creating an empty database file if it doesn't yet exist

            if [ ! -f "${database}" ]; then

              exit 0;

            fi

            echo "Deleting query logs older than ${days} days"

            ${getExe cfg.package} sqlite3 "${database}" "DELETE FROM query_storage WHERE timestamp <= CAST(strftime('%s', date('now', '-${days} day')) AS INT); select changes() from query_storage limit 1"

          '';