[gdk-pixbuf] ico: Avoid possible ImageScore overflow

[Bastien Nocera <hadess src gnome org>]

commit 99508c712d50e691328f47ce137cdbfa48b2d2e7
Author: Bastien Nocera <hadess hadess net>
Date:   Thu Jul 13 22:05:36 2017 +0200

    ico: Avoid possible ImageScore overflow
    
    Seeing as this is only a comparison, don't try to do arithmetics that
    could overflow.
    
    Detected by UBSan:
    io-ico.c:204:9: runtime error: signed integer overflow: 2134193699 -
    -555819298 cannot be represented in type 'int'
    
    https://bugzilla.gnome.org/show_bug.cgi?id=776040

 gdk-pixbuf/io-ico.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/gdk-pixbuf/io-ico.c b/gdk-pixbuf/io-ico.c
index ddb804c..9e5cce2 100644
--- a/gdk-pixbuf/io-ico.c
+++ b/gdk-pixbuf/io-ico.c
@@ -203,7 +203,11 @@ compare_direntry_scores (gconstpointer a,
        const struct ico_direntry_data *ib = b;
 
        /* Backwards, so largest first */
-       return ib->ImageScore - ia->ImageScore;
+       if (ib->ImageScore > ia->ImageScore)
+               return -1;
+       else if (ib->ImageScore < ia->ImageScore)
+               return 1;
+       return 0;
 }
 
 static void DecodeHeader(guchar *Data, gint Bytes,