cleaned up BasePlot.__sat_bounds code
cleaned up BasePlot.__sat_bounds code

CoolProp/CoolProp-museum,ibell/coolprop,CoolProp/CoolProp-museum,CoolProp/CoolProp-museum,ibell/coolprop,CoolProp/CoolProp-museum,CoolProp/CoolProp-museum,ibell/coolprop,ibell/coolprop,ibell/coolprop,ibell/coolprop,ibell/coolprop,CoolProp/CoolProp-museum,CoolProp/CoolProp-museum,ibell/coolprop