IndigoException when generating a simple InChI from SMILES

**Summary**
Can't generate inchi for some simple molecules (e.g. "CCC")

**Steps to Reproduce**
```
from indigo import inchi, Indigo
indigo = Indigo()
indigo_inchi = inchi.IndigoInchi(indigo)

m = indigo.loadMolecule("CCC")

assert indigo_inchi.getInchi(m) is not None
assert indigo_inchi.getInchiKey(m) is not None
```
**Expected behavior**
`InChI=...` (proper inchi string for "CCC")

**Actual behavior**
IndigoException is raised:
```
indigo.indigo.indigo_exception.IndigoException: core: can not access object #2: _Map_base::at
```
**Environment details:**
- epam.indigo==1.18.0
- AWS EC2 r6g (arm64)
- python 3.11.7

Start by running the Python reproduction with epam.indigo 1.18.0 on the reported environment, focusing on IndigoInchi.getInchi and getInchiKey for the SMILES "CCC". Trace the failing path that raises the _Map_base::at exception; done means both calls return a valid InChI string and key without raising IndigoException.

Written by the indexing model from the issue text.