Fix mass density in REFPROP for vapor phase; closes #1466
Fix mass density in REFPROP for vapor phase; closes #1466

CoolProp/CoolProp,CoolProp/CoolProp,CoolProp/CoolProp,henningjp/CoolProp,henningjp/CoolProp,henningjp/CoolProp,CoolProp/CoolProp,CoolProp/CoolProp,henningjp/CoolProp,CoolProp/CoolProp,henningjp/CoolProp,CoolProp/CoolProp,henningjp/CoolProp,henningjp/CoolProp,CoolProp/CoolProp,henningjp/CoolProp