Description:
------------
When preg_match() is called, I'm expecting that $matches will contain always one index per one capturing group. But when there is capturing group at the end of the pattern and it is not matched, $matches does not contain its index.


Test script:
---------------
$regexp = '/foo( bar)?/';
preg_match($regexp, 'foo', $matches);
print_r($matches);

Expected result:
----------------
Array (
  [0] => foo
  [1] =>
)

Actual result:
--------------
Array (
  [0] => foo
)