Low Pressure Saturation Calcs for HEOS::Water Failing after #2250

[henningjp]

Description

After #2250, low pressure water calculations I was using to test recent IF97 patch stopped working in HEOS::Water. Simple Saturation Temperature calculations now fail sporadically at low pressures. Returning other properties at low pressures also failing.

Steps to Reproduce

1. Set pressure below, say 10,000 Pa (0.010 MPa) but above Ptriple (611.655 Pa)
2. Calculate T at PQ state with Q = 0 or 1
3. At sporadic points along the curve, this simple calculation fails.

Expected behavior: (Prior to #2250 merge)

Actual behavior: (After #2250 merge)

Versions

CoolProp Version: 6.6.1dev
Operating System and Version: Windows
Access Method: Mathcad / Python - High-Level / Low-Level - Doesn't matter

Additional Information

I haven't tested any other fluids to see if this is reproduced there, but I suspect it is an issue for very low pressures for all fluids.

[henningjp]

While water is behaving the worst, some of the other fluids are experiencing this low-pressure behavior now relative to the fluids triple-point pressure.