Not recognized molfile v3000

If the molfile v3000 contains some SGroup (in this case label=CN), OCL seems not able to load the file.

I did a commit with an example https://github.com/cheminfo/openchemlib-js/commit/b224f876b4d1b9c32f4b157098c00d75b6dc0a17

```
openchemlib-js [main●] % node examples/v3000/load.js
molecule 0
moleculeNoSGroup 3
moleculeV2000 3
```

It is expected to give 3 times '3' and the first 'molecule' has '0' atoms.

@targos are you able to test with the last version ?

Start with the reproduction in examples/v3000/load.js and the example file introduced by commit b224f876b4d1b9c32f4b157098c00d75b6dc0a17. Run it to confirm that the SGroup-containing v3000 molfile reports zero atoms while the other two cases report three; done means all three cases report three atoms.

Written by the indexing model from the issue text.