Fixed incorrect call to WriteBlob reported in #490.

Dirk Lemstra · Dirk Lemstra · commit 72f5c8632bff · 2017-05-15T21:17:59.000+02:00
diff --git a/coders/png.c b/coders/png.c
@@ -4477,10 +4477,11 @@ static Image *ReadOneJNGImage(MngInfo *mng_info,
           (void) LogMagickEvent(CoderEvent,GetMagickModule(),
             "    Copying JDAT chunk data to color_blob.");
 
-        (void) WriteBlob(color_image,length,chunk);
-
         if (length != 0)
-          chunk=(unsigned char *) RelinquishMagickMemory(chunk);
+          {
+            (void) WriteBlob(color_image,length,chunk);
+            chunk=(unsigned char *) RelinquishMagickMemory(chunk);
+          }
 
         continue;
       }
