undefined variable `h5f_file` in `src/Ions.cc`

[dreamer2368]

writeData2D in src/Ions.cc uses an undefined variable h5f_file:

template <typename T>
void writeData2d(hid_t file_id, std::string datasetname, std::vector<T>& data,
    const int n, T element)
{
#ifdef MGMOL_USE_HDF5P
    if (h5f_file.useHdf5p())
    {
        // fill up data array to dimension common to all tasks
        short s = data.size();
        short ms;
        mgmol_tools::allreduce(&s, &ms, 1, MPI_MAX, h5f_file.comm_active());
        for (short i = s; i < ms; i++)
            data.push_back(element);
        size_t dims[2] = { data.size() / n, n };

        mgmol_tools::parallelWrite2d(
            file_id, datasetname, data, dims, h5f_file.comm_active());
    }
    else
#endif
    {
        size_t dims[2] = { data.size()/n, n };
        mgmol_tools::write2d(file_id, datasetname, data, dims);
    }
}

This causes a compile-time error when MGMOL_USE_HDF5P is enabled.

[dreamer2368]

Addressed by #231 .