Handle edge case in utils.py

[amorehead]

• Handles an edge case in utils.py that would normally lead to an RDKit-caused segmentation fault upon calling SplitMolByPDBResidues(mol) on certain molecule (single-fragment) inputs.

[exs-cbouy]

Hi @amorehead and thanks for opening a PR, it's really appreciated 🙌

Regarding the issue, I've only encountered the segmentation fault when the input mol was missing residue information for SplitMolByPDBResidues to function correctly.
There's already the prolif.Molecule.from_rdkit method to wrap around this problem by adding dummy residue info, is that enough to fix your problem?

[amorehead]

Hi, @exs-cbouy. Thanks for pointing out that this issue can be avoided by using prolif.Molecule.from_rdkit! In which case, I think we can close this issue, as that resolves the root concern on my end.