[gimp] plug-ins: fix #8553 GIMP 2.99.12 Cannot Open WebP Files

[Jacob Boerema <jboerema src gnome org>]

commit 85134478c765c1adaa3c0d49ea8159fe8587651d
Author: Jacob Boerema <jgboerema gmail com>
Date:   Tue Aug 30 15:33:04 2022 -0400

    plug-ins: fix #8553 GIMP 2.99.12 Cannot Open WebP Files
    
    GIMP tried to open webp files as ani (animated cursor) files. The reason
    for this is that for ani we had set the file magic as the first 4 bytes
    should be RIFF.
    
    However, RIFF is a container format, used by many different file formats,
    among which is also webp.
    This means that checking for RIFF is not specific enough.
    
    Based on the info on http://fileformats.archiveteam.org/wiki/ANI
    we will check the 4 bytes starting at offset 8 for ACON, which is
    apparently the identifying part for animated icons.

 plug-ins/file-ico/ico.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/plug-ins/file-ico/ico.c b/plug-ins/file-ico/ico.c
index 0b4efda25d..5693d619e6 100644
--- a/plug-ins/file-ico/ico.c
+++ b/plug-ins/file-ico/ico.c
@@ -242,7 +242,7 @@ ico_create_procedure (GimpPlugIn  *plug_in,
       gimp_file_procedure_set_extensions (GIMP_FILE_PROCEDURE (procedure),
                                           "ani");
       gimp_file_procedure_set_magics (GIMP_FILE_PROCEDURE (procedure),
-                                      "0,string,RIFF");
+                                      "8,string,ACON");
 
       gimp_load_procedure_set_thumbnail_loader (GIMP_LOAD_PROCEDURE (procedure),
                                                 LOAD_ANI_THUMB_PROC);