Description:
------------
When the string end with full-width character and its width is one greater than the desired trimming width，trimmaker is alse a half-width character, which will cause mb_strimwidth not to trim.

Affects all stable versions of PHP.

Test script:
---------------
<?php
echo mb_strimwidth("一二三", 0, 4, '.', 'UTF-8')."\n";
echo mb_strimwidth("一二三", 0, 5, '.', 'UTF-8')."\n";
echo mb_strimwidth("一二三", 0, 6, '.', 'UTF-8')."\n";
echo mb_strimwidth("abcdef", 0, 4, '.', 'UTF-8')."\n";
echo mb_strimwidth("abcdef", 0, 5, '.', 'UTF-8')."\n";
echo mb_strimwidth("abcdef", 0, 6, '.', 'UTF-8')."\n";

Expected result:
----------------
一.
一二.
一二三
abc.
abcd.
abcdef

Actual result:
--------------
一.
一二三
一二三
abc.
abcd.
abcdef