More MPI Bugs

When I execute the getting_started_3.py script with MPI mpiexec -n 2 python getting_started_3.py I get the following error message:

Traceback (most recent call last):
  File "/home/jakob/nifty/demos/getting_started_3.py", line 163, in <module>
    main()
  File "/home/jakob/nifty/demos/getting_started_3.py", line 153, in main
    [pspec.force(mock_position), samples.average(logspec).exp()],
  File "/home/jakob/nifty/nifty8/minimization/sample_list.py", line 306, in average
    return utilities.allreduce_sum(res, self.comm) / n
  File "/home/jakob/nifty/nifty8/utilities.py", line 371, in allreduce_sum
    vals[j] = vals[j] + comm.recv(source=who[j+step])
  File "/home/jakob/nifty/nifty8/field.py", line 726, in func2
    return self._binary_op(other, op)
  File "/home/jakob/nifty/nifty8/field.py", line 689, in _binary_op
    utilities.check_object_identity(other._domain, self._domain)
  File "/home/jakob/nifty/nifty8/utilities.py", line 419, in check_object_identity
    raise ValueError(f"Mismatch:\n{obj0}\n{obj1}")
ValueError: Mismatch:
DomainTuple, len: 1
* PowerSpace(harmonic_partner=RGSpace(shape=(128, 128), distances=(1.0, 1.0), harmonic=True), binbounds=None)
DomainTuple, len: 1
* PowerSpace(harmonic_partner=RGSpace(shape=(128, 128), distances=(1.0, 1.0), harmonic=True), binbounds=None)

When executing without MPI I get no error.