brighter but not near saturated stars with core pixels NAN due to scaling using COMP_WT

[Mark Huber]

Originally found in ppSub save-revconv output *.refConv.wt:
diff_id=272923, skycell.052 for MD10.20120818
that is a fairly deep and down-scaled refstack to warp in a WARPSTACK diffim.

Core pixels of brighter sources are outside the allowed data value in the compressed FITS and set to NAN. As the refConv.wt FITS are basically used only for magic, may not be critical priority if magic not in use. Unknown if issue in other compressed files.