Segfault with bad values of max_radial/max_angular

[Luthaf]

Another discovery by @bananenpampe. The following code segfaults:

from rascal.representations import SphericalInvariants

hypers = {
    "soap_type": "PowerSpectrum",
    "interaction_cutoff": 3,
    "radial_basis": "GTO",
    "max_radial": 0,
    "max_angular": 9,
    "gaussian_sigma_constant": 0.3,
    "gaussian_sigma_type": "Constant",
    "cutoff_function_type": "ShiftedCosine",
    "cutoff_smooth_width": 0.5,
    "normalize": True,
}

soap = SphericalInvariants(**hypers)

I think this should throw an error instead!

---

Other invalid combinations:

max_radial	max_angular	expected	actual
1	0	OK	OK
0	1	Error	segfault
0	0	Error	segfault
0	-1	Error	segfault
1	-1	Error	segfault
1	-3	Error	std::bad_alloc
-1	1	Error	std::bad_alloc

[agoscinski]

I am working on a PR making the json reading of cpp files more user friendly #376 (at the moment json error is returned which basically only tells you that somewhere in the hypers there is a parameter wrong). I can add also checks for max_angular and max_radial

[agoscinski]

so annoying, on the c++ side we use size_t, so one has to do the check on the python side. I really think size_t is always a bad choice for user input

EDIT: I can also read temporary an int and then convert it to size_t