From 263cd4519f45bc6ecde74ee280eb1d68ee2de642 Mon Sep 17 00:00:00 2001
From: Eddie Kohler <ekohler@gmail.com>
Date: Sat, 2 Dec 2017 23:10:30 -0500
Subject: [PATCH] Two GIFs with zero images are the same.

Another KAIST report; we null-dereferenced previously.
---
 src/gifdiff.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/gifdiff.c b/src/gifdiff.c
index 04721d8..40da3c1 100644
--- a/src/gifdiff.c
+++ b/src/gifdiff.c
@@ -248,12 +248,6 @@ compare(Gif_Stream *s1, Gif_Stream *s2)
   Gif_CalculateScreenSize(s1, 0);
   Gif_CalculateScreenSize(s2, 0);
 
-  if (s1->nimages != s2->nimages
-      && (s1->nimages == 0 || s2->nimages == 0)) {
-    different("frame counts differ: <#%d >#%d", s1->nimages, s2->nimages);
-    return DIFFERENT;
-  }
-
   if (s1->screen_width != s2->screen_width
       || s1->screen_height != s2->screen_height) {
     different("screen sizes differ: <%dx%d >%dx%d", s1->screen_width,
@@ -268,6 +262,14 @@ compare(Gif_Stream *s1, Gif_Stream *s2)
     return DIFFERENT;
   }
 
+  if (s1->nimages == 0 || s2->nimages == 0) {
+    if (s1->nimages != s2->nimages) {
+      different("frame counts differ: <#%d >#%d", s1->nimages, s2->nimages);
+      return DIFFERENT;
+    } else
+      return SAME;
+  }
+
   /* Create arrays for the image data */
   screen_width = s1->screen_width;
   screen_height = s1->screen_height;