Description:
------------
When executing preg_replace on a string over 32,205 bytes and no double line breaks with the following expression, the function neither matches nor returns the original string. preg_last_error() doesn't indicate any  preg related errors.

Reproduce code:
---------------
 error_reporting(E_ALL);
  $original_string = "This is a preg_replace bug.\n";
  $string = '';
  $i = 0;
  while($i < 1177) {
    $string .= $original_string;
    preg_replace('/\n?(.+?)(?:\n\s*\n|\z)/s', "foo", $string,-1,$count);
    if($count == 0) {
      echo "I broke at count: $i\n";
      exit;
    }
    $i++;
  }
  echo "I didn't break at count: $i\n";
  echo preg_last_error();


Expected result:
----------------
I didn't break at count: 1176.

Actual result:
--------------
I broke at count: 1176