Dataset not properly initialized ?

**Describe the bug**
Dataset class not properly initialised

**To Reproduce**
trying c++ code from the repository, 1D domain decompostion/particle
```
Dataset dataset = Dataset(determineDatatype(), {mpi_size});

if (0 == mpi_rank)
cout << "Prepared a Dataset of size " << dataset.extent[0] << " x "
<< dataset.extent[1] << " and Datatype " << dataset.dtype
<< '\n';
```
** obtained output **
`Prepared a Dataset of size 50 x 47760564901816 and Datatype DOUBLE`
seems that dataset.extend[1] is not initialised?