ResonanceMolSupplier can fail with small maxStructs values

[greglandrum]

Here are a couple of examples:

In [3]: from rdkit import Chem 
   ...: mol = Chem.MolFromSmiles('CC(C)C(C(=O)OC(C#N)c1cccc(Oc2ccccc2)c1)c3ccc(OC(F)F)cc3') 
   ...: len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 5))                                                
Out[3]: 5

In [4]: len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 3))                                                
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-4-67b3948cbeb1> in <module>
----> 1 len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 3))

RuntimeError: idx = 0, d_ceVect.size() = 0

In [5]: mol = Chem.MolFromSmiles('c1cccnc1CCc1ccncc1')                                                                      

In [6]: len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 3))                                                
Out[6]: 3

In [7]: len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 2))                                                
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-7-1973ad78917d> in <module>
----> 1 len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 2))

RuntimeError: idx = 0, d_ceVect.size() = 0

In [8]: len(Chem.ResonanceMolSupplier(mol, Chem.KEKULE_ALL, maxStructs = 3))                                                
Out[8]: 3

[ptosco]

@greglandrum I'll have a look later today or tomorrow.

[greglandrum]

Thanks @ptosco