Description:
------------
Seems preg_match with /u modifier corrupts process memory or returns pointer to nirvana instead of pointer to a string.

Reproduce code:
---------------
<?
preg_match('/(.{0,20})$/us', " ", $m);
var_export($m);
?>

Expected result:
----------------
space

Actual result:
--------------
something like

array ( 
  0 => ' kjwekwjn',
  1 => ' wereinoiu',
)

where "kjwekwjn" and "wereinoiu" are random strings with random binary data (useless to copy-paste them here).