[Finder] Fixed filter size on directory

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | not sure
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | itself
| License       | MIT
| Doc PR        | n/a

Right now Finder composant returns all directories even is a size() is set and should filter out some.

Before the fix : 
```php
$finder->directories()->size('< 500') 
// => return all folders even those bigger then 500ko
```
After 
```php
$finder->directories()->size('< 500') 
// => only returns folders smaller than 500ko
```
Not sure if it can break BC, need your feedbacks