Fix ThermoPhase::getElementPotentials and setElementPotentials
Fix ThermoPhase::getElementPotentials and setElementPotentials

Broken in r2719.

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