incorrect NaN when load fz image

[acdo2002]

Describe the bug
Loading "M17_SWex.fits.fz", the surrounding NaN values become negative float numbers instead of NaN.
Please compare "M17_SWex.fits.fz" and "M17_SWex.fits" in the carta.
If we use ds9 to read "M17_SWex.fits.fz", the surrounding NaN values are still NaN.
The images can be found in here

To Reproduce
Steps to reproduce the behavior:

1. Open "M17_SWex.fits.fz", you can directly see the difference to "M17_SWex.fits"

Method to produce "M17_SWex.fits.fz":
I used cfitsio-4.1.0, ./fpack -g M17_SWex.fits

Expected behavior
The surrounding values of "M17_SWex.fits.fz" should be NaN.

Screenshots or videos

Platform info (please complete the following information):

• OS [e.g. macOS Monterey]: Ubuntu 20.04
• Browser [e.g. chrome, safari, electron app]: chrome
• Browser version [e.g. 22]: Version 102.0.5005.61
• Backend branch [e.g. dev, v3b2 release]: v3b3
• Frontend branch [e.g. dev, v3b2 release]: v3b3