Prevent a buffer overrun if the comment begins with a literal quote character and...

Prevent a buffer overrun if the comment begins with a literal quote character and the string exceeds 65k characters.  Also prevent comments longer than 65k characters from being written, since this will produce an incorrect JPEG file.

git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@1323 632fc199-4ca6-4c93-a231-07263d6284db