port upstream fix for local buffer overflow

More info here:
http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=26482&sid=81658bc2f51a8d9893279cd01e83783f
http://sourceforge.net/p/libjpeg-turbo/code/1425/


Fix Huffman local buffer overrun discovered by Debian developers when
attempting to transform a junk image using ImageMagick:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=768369