fixes initializing attributes in Sort class

If you set all the parameters of sorting...
```php
 'age' => array(
     'asc' => array('age' => Sort::ASC),
     'desc' => array('age' => Sort::DESC),
     'default' => Sort::ASC,
     'label' => Inflector::camel2words('age'),
 )
```
then this element will not get into the final configuration array