FieldParser: fix oversight of not adding parsed fields to map for APF format files

            auto file_type = guess_file_type(path);

            LOG(DEBUG) << "Assuming file type \"" << (file_type == FileType::APF ? "APF" : "INIT") << "\"";

            FieldData<T> field_data;

            switch(file_type) {

            case FileType::INIT:

                if(units.empty()) {

                    LOG(WARNING) << "No field units provided, interpreting field data in internal units, this might lead to "

                                    "unexpected results.";

                }

                return parse_init_file(file_name, units);

                field_data = parse_init_file(path, units);

                break;

            case FileType::APF:

                if(!units.empty()) {

                    LOG(DEBUG) << "Units will be ignored, APF file content is interpreted in internal units.";

                }

                return parse_apf_file(file_name);

                field_data = parse_apf_file(path);

                break;

            default:

                throw std::runtime_error("unknown file format");

            }

            // Store the parsed field data for further reference:

            field_map_[path] = field_data;

            return field_data;

        }

    private:

            }

            LOG_PROGRESS(INFO, "read_init") << "Reading field data: finished.";

            FieldData<T> field_data(

            return FieldData<T>(

                header, std::array<size_t, 3>{{xsize, ysize, zsize}}, std::array<T, 3>{{xpixsz, ypixsz, thickness}}, field);

            // Store the parsed field data for further reference:

            field_map_[file_name] = field_data;

            return field_data;

        }

        size_t N_;