Placate XCode by fixing is_inside function

Closes https://github.com/CoolProp/CoolProp/issues/261

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>

src/Backends/Helmholtz/PhaseEnvelopeRoutines.cpp

@@ -486,6 +486,9 @@ bool PhaseEnvelopeRoutines::is_inside(HelmholtzEOSMixtureBackend &HEOS, paramete
             throw ValueError("For now can't be inside");
         }
     }
+	else{
+		throw ValueError("You have a funny number of intersections in is_inside");
+	}
 }
 
 } /* namespace CoolProp */