bug#37370: 27.0.50; gnus-article-view-part duplicates Attachment: headers

[Jose A. Ortega Ruiz]

- Open any mulitpart email (html and text), with butonize set so that
  you see the () text/plain (*) text/html buttons
- Press `b' (gnus-article-view-part) in the summary buffer or the
  article buffer
- A new Attachment: header, duplicating existing ones, appears when
  switching the view
- This keeps going on, every time one presses b again... e.g., after two
  times is see at the end of the mail headers:

     Date: Tue, 10 Sep 2019 11:28:21 +0200 (4 hours, 24 minutes, 19 seconds ago)
     Attachment: [2. text/plain]...
     Attachment: [3. text/html]...
     Attachment: [2. text/plain]...

     1.  ( ) text/plain          (*) text/html           

Thanks!



In GNU Emacs 27.0.50 (build 17, x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2019-09-10 built on imladris
Repository revision: 74e9799bd89484b8d15bdd6597c68fc00d07e7f7
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux bullseye/sid

Recent messages:
nnimap read 0k from localhost
Do you really want to delete these 2 articles forever? (y or n) y
nnimap read 0k from localhost
Expiring articles...done
nnimap read 0k from localhost
uncompressing gnus-art.el.gz...done
Note: file is write protected
uncompressing gnus-art.el.gz...done
Searched 0/1 files
Searched 1/1 files
Quit
Configured using:
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