The following link explains the issue in detail:

http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=23117

--------------------------------------------------------------------------------

--- ImageMagick-6.8.3/coders/url.c	Mon Dec 10 05:09:00 2012

+++ ImageMagick-6.8.3/coders/url.c	Mon Apr 22 00:07:50 2013

@@ -154,12 +154,9 @@

     file=fdopen(unique_file,"wb");

   if ((unique_file == -1) || (file == (FILE *) NULL))

     {

-      read_info=DestroyImageInfo(read_info);

-      (void) CopyMagickString(image->filename,read_info->filename,

-        MaxTextExtent);

       ThrowFileException(exception,FileOpenError,"UnableToCreateTemporaryFile",

-        image->filename);

-      image=DestroyImageList(image);

+        read_info->filename);

+      read_info=DestroyImageList(read_info);

       return((Image *) NULL);

     }

   (void) CopyMagickString(filename,image_info->magick,MaxTextExtent);