bug#39994: 27.0.90; Broken image-converter probe for imagemagick

[Juri Linkov]

>> Then I tried imagemagick, but image-converter said .ico format is 
>> unsupported.
>> Whereas running `convert -list format` outputs:
>>
>>    Format  Module    Mode  Description
>> -------------------------------------------------------------------------------
>>       ICO* ICON      rw+   Microsoft icon
>>
>> So this patch adds the support for the 'Module' column to imagemagick probe:
>
> Ah, so some versions have an additional column in there?  My convert
> -list format outputs:
>
>       ICO* rw+   Microsoft icon

Maybe because my version is too old:
ImageMagick 6.9.7-4 Q16 x86_64 20170114

>>  (defvar image-converter--converters
>>    '((graphicsmagick :command ("gm" "convert") :probe ("-list" "format"))
>> -    (ffmpeg :command "ffmpeg" :probe "-decoders")
>> -    (imagemagick :command "convert" :probe ("-list" "format")))
>> +    (imagemagick :command "convert" :probe ("-list" "format"))
>> +    (ffmpeg :command "ffmpeg" :probe "-decoders"))
>>    "List of supported image converters to try.")
>
> Was this part included by mistake?  It changes the order the converters
> are tested.

I propose to change the order because ffmpeg doesn't support too much
image formats, so it is less useful than imagemagick when both
imagemagick and ffmpeg are installed at the same time.

>>          ;; Lines look like
>>          ;; "      WPG* r--   Word Perfect Graphics".
>> -        (while (re-search-forward "^ *\\([A-Z0-9]+\\)\\*? +r" nil t)
>> +        (while (re-search-forward "^ *\\([A-Z0-9]+\\)\\*?\\(?: 
>> +[A-Z0-9]+\\)? +r" nil t)
>
> Look OK to me, but the comment should be amended to reflect the two
> different line formats it's now matching.

Oh, I haven't noticed the comment, I don't know why, now updated:

diff --git a/lisp/image/image-converter.el b/lisp/image/image-converter.el
index 0488a13d41..3d74b8b30c 100644
--- a/lisp/image/image-converter.el
+++ b/lisp/image/image-converter.el
@@ -149,8 +149,9 @@ image-converter--probe
       (when (re-search-forward "^-" nil t)
         (forward-line 1)
         ;; Lines look like
-        ;; "      WPG* r--   Word Perfect Graphics".
-        (while (re-search-forward "^ *\\([A-Z0-9]+\\)\\*? +r" nil t)
+        ;; "      WPG* r--   Word Perfect Graphics" or
+        ;; "      WPG* WPG       r--   Word Perfect Graphics".
+        (while (re-search-forward "^ *\\([A-Z0-9]+\\)\\*?\\(?: +[A-Z0-9]+\\)? 
+r" nil t)
           (push (downcase (match-string 1)) formats)))
       (nreverse formats))))