Possible fix fo inhale_pp ratio

Some things about var/ratio used when inhale_pp < safe_pressure_min didn't make sense, and I'm thinking this is a possible error.

I think the amount of gas used should decrease with inhale_pp as, after all the oxyloss is being caused by the fact that fewer moles of a necessary gas are entering the bloodstream. In any case, it was very strange that the amount of inhaled gas used approached infinity as inhale_pp went to zero.

Also, if inhale_pp < safe_pressure_min then safe_pressure_min/inhale_pp is always > 1, but HUMAN_MAX_OXYLOSS = 1.