[BUG] Exceptions if image extension does not contain a pixel plane.

[teald]

Describe the bug
Images lacking a pixel plane will raise an IndexError if some functions (e.g., .info) are called.

To Reproduce
Steps and requirements to reproduce the behavior:

1. Try to load in a file with image extensions lacking a pixel plane (see attached file)
2. Load the file using from_file
3. Try to

Expected behavior
From Chris:

I think ext.data or ext.mask or ext.variance should all return None for such an extension. It's slightly cleaner than having ext.data crash and is entirely reasonable (ImageHDU.data returns None in such a case).
ad.info should probably say something simple like

Index  Content                  Type              Dimensions     Format
[ 0]   science                  NDAstroData       (2048, 2048)   float32
[ 1]   science                  NDAstroData       (2048, 2048)   float32
[ 2]   none```

Example code
Assuming you have this data from the archive in the local directory.

from astrodata import from_file

data = from_file("S20231217S0093.fits")
data.info()

Screenshots
N/A

Desktop (please complete the following information):

• OS: OSX
• Version Ventura 13.5

Additional context
N/A