fix support for breakup in 2D kinematic env example

[slayoo]

it's a regression introduced in #1371 which was not caught by CI due to lack of test coverage
will break in:
https://github.com/open-atmos/PySDM/blob/main/examples/PySDM_examples/Szumowski_et_al_1998/simulation.py#L115-L116

[AgnieszkaZaba]

Should we add separate settings file for this example?

[slayoo]

Yes, I'd say we could try to move the GUI logic out of the Arabas_et_al_2015 example as it has little relevance to the paper.

It would be best to provide a non-GUI notebook in this example that reproduces results close to the paper (i.e., the new settings file), while moving the GUI elsewhere (perhaps to tutorials?) and equipping it with tests covering all conditional cases.