fix: RuntimeError if batch has only invalid mols

[jannisborn]

Fixes #83

For the future, I think that for the property optimization, it would be even better if max_resample can be controlled by the user.
Maybe having an optional task_kwargs that defaults to {} could be passed to GCPNGeneration and specify hyperparameters for the property optimization.

[KiddoZhu]

That sounds like a good idea. We will add that as a part of property optimization.

[jannisborn]

Hi @KiddoZhu
do you plan to make a new release with the bugfixed code? It would be nice to have a functional stable release.

[KiddoZhu]

Yes. We will get a new release soon, probably in one or two weeks.