Possibly wrong message is reported when a FITS image has only one HDU.

[rmorales]

Summary:
Possibly wrong message is reported when a FITS image has only one HDU.

gnuastro version:
0.11

test image set:
https://cloud.iaa.csic.es/public.php?service=files&t=9344cdb85c640c7dd74446d8c266591d

command:
aststatistics 019_00.fits

result :
‘019_00.fits’ has only one extension/HDU but you have asked for the 
second HDU (hdu number 1 in CFITSIO) ....
…
Gnuastro leaves the first HDU blank (with no data) and writes the 
outputs in the second HDU.
...
This is the recommended way in the FITS standard.
...

question:
Maybe I’m wrong, but I did not find any recommendation in the last FITS 
standard to organize the FITS file in that way.

FITS standard: Version 4.0 (13 August 2018)
https://fits.gsfc.nasa.gov/standard40/fits_standard40aa-le.pdf
Section 3. FITS file organization

Using fitsverify also does not report any error or warning on the same 
file.