bug#56375: 28.1.50; Calling "convert" from thumbs.el is broken

[Benjamin Riefenstahl]

* dired to a directory with images that are larger than 100x100 pixels

* M-x thumbs-dired-show

* I get a buffer with the first few images in the directory in their
  original size

* I expect the images to be scaled to thumbs smaller than 100x100,
  see thumbs-geometry

Tracing the code I stumble onto thumbs-call-convert.  Some time in the
past this was converted from using the shell to passing the parameters
directly, but the fallout was not handled correctly.

I will post a patch as a follow-up.

----

In GNU Emacs 28.1.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, cairo 
version 1.16.0)
 of 2022-05-12 built on zenobia
Repository revision: f03c5d81bd4a7af1364558b406e2b87a78b3af73
Repository branch: emacs-28
System Description: Debian GNU/Linux 11 (bullseye)

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Group

Minor modes in effect:
  gnus-topic-mode: t
  gnus-undo-mode: t
  desktop-save-mode: t
  display-time-mode: t
  xclip-mode: t
  xterm-mouse-mode: t
  delete-selection-mode: t
  cua-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
~/Projects/ttf-mode/arc-mode-compat hides ~/emacs/arc-mode-compat
/home/benny/.emacs.d/elpa/transient-20210920.1038/transient hides 
/usr/local/share/emacs/28.1.50/lisp/transient
/home/benny/site-lisp/dictionary-1.10/dictionary hides 
/usr/local/share/emacs/28.1.50/lisp/net/dictionary

Features:
(shadow bbdb-message emacsbug dired-aux gnus-html help-fns bookmark
gnus-kill nnselect gnus-search eieio-opt speedbar ezimage dframe
find-func nndoc flow-fill misearch multi-isearch smerge-mode diff
compile descr-text cus-start termshape shr-color color format-spec
benny-nitter eww xdg url-queue thingatpt benny-url sort gnus-cite
mail-extr gnus-bcklg gnus-async gnus-dup gnus-ml pp gnus-topic jka-compr
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gnus-spec gnus-int gnus-range message rmc puny rfc822 mml mml-sec epa
epg rfc6068 epg-config mm-decode mm-bodies mm-encode mailabbrev
gmm-utils mailheader gnus-win gnus nnheader gnus-util rmail
rmail-loaddefs text-property-search wid-edit mule-util imenu time-date
desktop frameset highline benny-calendar-cfg ange-ftp comint ansi-color
ring generic-x autoinsert cc-mode cc-fonts cc-guess cc-menus cc-styles
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xt-mouse cal-china lunar solar cal-dst cal-bahai cal-islam cal-hebrew
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hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 361711 129281)
 (symbols 48 39764 19)
 (strings 32 212367 23946)
 (string-bytes 1 6513504)
 (vectors 16 52664)
 (vector-slots 8 1676247 215016)
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 (intervals 56 1742 1237)
 (buffers 992 29))