Merge pull request #175 from TheoChem-VU/174-issue-with-writing-molec…

…ules-when-the-molecule-does-not-have-a-comment-variable

Now checking if the molecule has a comment attribute or not

src/tcutility/molecule.py

@@ -39,7 +39,7 @@ def save(mol: plams.Molecule, path: str, comment: str = None):
     """Save a molecule in a custom xyz file format.
     Molecule and atom flags can be provided as the "flags" parameter of the object (mol.flags and atom.flags).
     """
-    comment = comment or mol.comment
+    comment = comment or mol.comment if hasattr(mol, 'comment') else ''
     with open(path, "w+") as f:
         f.write(f"{len(mol.atoms)}\n{comment}\n")
         for atom in mol.atoms: