Fix preg_match_all requiring three parameters

`preg_match_all`'s third parameter (`$matches`) should be an optional parameter.

Example:

```php
<?php
var_dump(preg_match_all('/o/', 'Hello World'));
```

**HHVM Output:**

```
HipHop Warning: preg_match_all() expects exactly 2 parameters, 1 given in /var/share/php/preg.php on line 8
NULL
```

**Correct Output:**

```
int(2)
```

**Notes:**

Just an FYI as to why I added a new if statement, doing a `continue` at that point in the loop was skipping a few things at the end, which caused an infinite loop.