Making a deepcopy breaks cosmo_array.to_physical()

[mladenivkovic]

        data = swiftsimio.load(snapshot_name)
        gas = data.gas

        u = gas.internal_energies

        #  print(u[:1])
        #  [0.00100253] 1.0459449255936e-6*Mpc**2/Gyr**2 (Comoving)

        u1 = copy.deepcopy(u)

        #  print(u1[:1])
        #  [1.0485887e-15] kpc**2/kyr**2 (Comoving)

        #  print(type(u1))
        # <class 'swiftsimio.objects.cosmo_array'>

        u1.to_physical()

        #  Traceback (most recent call last):
        #    File "/home/mivkov/Downloads/CosmoHeatingTest_zipped/./plotSolution.py", line 280, in <module>
        #      t, T, mu, mass_fraction, u, photon_energies = get_snapshot_data(snaplist)
        #    File "/home/mivkov/Downloads/CosmoHeatingTest_zipped/./plotSolution.py", line 213, in get_snapshot_data
        #      u1.to_physical()
        #    File "/home/mivkov/local/swiftsimio/swiftsimio/objects.py", line 907, in to_physical
        #      copied_data.convert_to_physical()
        #    File "/home/mivkov/local/swiftsimio/swiftsimio/objects.py", line 892, in convert_to_physical
        #      values *= self.cosmo_factor.a_factor
        #  AttributeError: 'NoneType' object has no attribute 'a_factor'

[MatthieuSchaller]

Possibly also one issue that will be solved by the changes @robjmcgibbon is looking at.