Astrometry.net 0.88: fix issue on recent Mac OSX

People have reported (https://groups.google.com/g/astrometry/c/F0P5yoxvyNk/m/WpehXN22AgAJ?utm_medium=email&utm_source=footer&pli=1) issues related to handling inf values (HUGE_VAL in the code), since we use --finite-math-only. This fix removes the use of HUGE_VAL as a default signalling value.

There shouldn't be any functional changes for anyone else.