Fix support not-asscii characters with mbstring.func_overload setting

I catch and fix problem with not-ascii characters, similar to #38 issue. 
Similar problem: https://bugs.php.net/bug.php?id=49790

My PHP Version 5.5.12
Testing environment for ``php.ini`` (``.htaccess`` not affected):
``mbstring.func_overload = 7``
``mbstring.internal_encoding = UTF-8``