[clib] Fix bounds check on getMolecularWeights
[clib] Fix bounds check on getMolecularWeights

The incorrect bounds check here caused problems with phases where
there were more elements than species.

Fixes Issue 173.


imitrichev/cantera,imitrichev/cantera,imitrichev/cantera,Heathckliff/cantera,Heathckliff/cantera,imitrichev/cantera,imitrichev/cantera,Heathckliff/cantera,Heathckliff/cantera,imitrichev/cantera,Heathckliff/cantera,Heathckliff/cantera