Negative size parameter (-1) in memcpy mbfl_strcut

How it was found

https://bugs.php.net/bug.php?id=71906

Memory corruption issue on mbstring extension, issue reported to PHP developers on 2016-03-26, fixed 2016-03-29 and released at 2016-03-31, affected PHP 5.5 , PHP 5.6 and PHP 7.

http://php.net/ChangeLog-5.php#5.5.34 http://php.net/ChangeLog-5.php#5.6.20 http://php.net/ChangeLog-7.php#7.0.5