bug#48324: 27.2; hexl-mode duplicates the UTF-8 BOM

[R. Diez]

> Ah, so maybe I didn't use the exact recipe.  I did try hexl-mode as
> well as hexl-find-file, but maybe I missed something.  Could someone
> please post an exact recipe, step by step?

I'll try again:

- I created an empty file with Caja (the MATE Desktop file manager) named 
Test7.txt . That empty file is 0 bytes long.
- I then dragged the file to Emacs in order to open it.
The default encoding is utf-8-unix (visible on Emacs' status line).
- I pressed my keyboard shortcut for (eval-expression).
- I changed the encoding by manually evaluating this expression:
(set-buffer-file-coding-system 'utf-8-with-signature-dos)
- I then typed in the buffer for Text7.txt the characters "123".
- I saved the buffer with menu "File", option "Save".
- I ran in the minibuffer command hexl-mode, which gives me the hex view for 
that file:
ef bb bf 31 32 33 0d 0a
- I moved the cursor with the arrow keys to the byte with value "31".
- I ran in the minibuffer command hexl-insert-hex-char, in order to overwrite 
the 31 with a new value.
- I typed in the minibuffer the hex value "00" (a binary null) and pressed 
enter.
- In the hex view, the BOM is now duplicated.

Best regards,
  rdiez