Fixed using condition without binding parameters and allow using an array for aliasing.

This PR fixes 2 things.

1. Previously, if we wanted to use the array form without an SQL snippet, it will fail:

```php
R::preload($beans, array('manager' => array('people')));
```
2. It fixes the ability to have conditional snippets without bindings:

```php
R::preload($beans, array('ownManager' => array('manager', array("name = 'john'"))))
```