File ImageMagick-CVE-2018-16749.patch of Package ImageMagick.8831

diff --git a/coders/png.c b/coders/png.c
index 31c0b8450..3d6eb7db2 100644
--- a/coders/png.c
+++ b/coders/png.c
@@ -4584,7 +4584,7 @@ static Image *ReadOneJNGImage(MngInfo *mng_info,
           (void) LogMagickEvent(CoderEvent,GetMagickModule(),
             "    Copying JDAT chunk data to color_blob.");
 
-        if (length != 0)
+        if ((length != 0) && (color_image != (Image *) NULL))
           {
             (void) WriteBlob(color_image,length,chunk);
             chunk=(unsigned char *) RelinquishMagickMemory(chunk);
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