MolToSmiles with doRandom=True raises errors with molecules containing fragments.

[greglandrum]

Discussed in #5371

^{Originally posted by claushofmann June 16, 2022}
Hi everyone,

I am new to Chemoinformatics and was playing around with rdkit for generating different random SMILES strings for the same molecule:

from rdkit import Chem
smiles = 'O=C([O-])c1ccccc1O.O=C([O-])c1ccccc1O.[Zn+2]'
mol = Chem.MolFromSmiles(smiles)
Chem.MolToSmiles(mol, doRandom=True, canonical=False)

For this specific molecule, I get this error:

RuntimeError: Range Error
	idx
	Violation occurred on line 206 in file Code/GraphMol/ROMol.cpp
	Failed Expression: 17 < 1
	RDKIT: 2022.03.3
	BOOST: 1_75