bug#43281: 27.1; Opening a bad GIF segfaults Emacs

[Robert Pluim]

>>>>> On Tue, 8 Sep 2020 20:38:30 +0700, nnoodle <nnoodle@chiru.no> said:

    nnoodle> To reproduce:
    nnoodle> $ echo 'GIF89a;' > bad.gif
    nnoodle> $ emacs -Q bad.gif

    nnoodle> The result will be a segmentation fault.

This should fix it, can you test it?

Thanks

Robert

diff --git a/src/image.c b/src/image.c
index d8c34669cc..6e3b71a869 100644
--- a/src/image.c
+++ b/src/image.c
@@ -8251,7 +8251,7 @@ gif_load (struct frame *f, struct image *img)
   Lisp_Object specified_file = image_spec_value (img->spec, QCfile, NULL);
   Lisp_Object specified_data = image_spec_value (img->spec, QCdata, NULL);
   EMACS_INT idx;
-  int gif_err;
+  int gif_err = 0;
 
   if (NILP (specified_data))
     {
@@ -8277,7 +8277,8 @@ gif_load (struct frame *f, struct image *img)
        {
 #if HAVE_GIFERRORSTRING
          image_error ("Cannot open `%s': %s",
-                      file, build_string (GifErrorString (gif_err)));
+                      file, gif_err ? build_string (GifErrorString (gif_err))
+                       : build_string ("Unknown error from gif library"));
 #else
          image_error ("Cannot open `%s'", file);
 #endif