Unsure hydrogen count

```
from indigo import Indigo

indigo = Indigo()
mol = indigo.loadMolecule('CCN(C1=NC(=CS1)CC(=O)NC2=CC=C(C=C2)Cl)C(=O)CCC(=O)[O-]')
atom = mol.getAtom(0)
r = mol.addAtom('Ar')
r.addBond(atom, 1)
print(mol.canonicalSmiles())
```
The above code gives error "SMILES saver: unsure hydrogen count on atom #26"
The problem is the added atom is not recognized as a pseudo atom. How to solve this issue?

Start by reproducing the Python snippet using Indigo, especially the addAtom, addBond, and canonicalSmiles calls. Trace how the added Ar atom is represented before serialization; done means the snippet treats it as a pseudo atom and canonicalSmiles completes without the unsure hydrogen count error.

Written by the indexing model from the issue text.