[Kinetics] Ensure that equilibrium constants are not zero
[Kinetics] Ensure that equilibrium constants are not zero

This prevents reverse rate constants from becoming NaN when the forward rate
constant underflows.


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