Fix ->validationErrors->count() when the object is null

Hi... in the **src/LaravelBook/Ardent/Ardent.php** line **541** i've found an issue: The `$this->validationErrors->count()` causes an error because `validationErrors` is null and does not retrive the `count()` method.

Then a single check if it's null, solve it... I do know how the object is null in my case, but here is my suggestion in this pull request.

Sorry about my poor english!