Optimiser occasional crashes with HDF5 enabled.

@ext-neveu_n reported crashes with the optimizer. It turned out that the crashes were coming from the HDF5 output (with ENABLEHDF5=FALSE there were no more crashes).

Stack trace:

H5PartWrapper::storeCavityInformation()
H5PartWrapper::open(int)
h5_open_file2
h5_error
h5_report_errorhandler

H5PartWrapper::open(int):

void H5PartWrapper::open(h5_int32_t flags) {
    close();

    h5_prop_t props = H5CreateFileProp ();
    MPI_Comm comm = Ippl::getComm();
    h5_err_t h5err = H5SetPropFileMPIOCollective (props, &comm);
#if defined (NDEBUG)
    (void)h5err;
#endif
    assert (h5err != H5_ERR);
    file_m = H5OpenFile (fileName_m.c_str(), flags, props);
    assert (file_m != (h5_file_t)H5_ERR);
    H5CloseProp (props);
}

So the opening of the file failed for some reason (Perhaps the optimiser has deleted the directory?).