Clear session from storage if no recaller can be found

[Boorinio]

Hello!

So, if somehow in your application you delete the authenticatable (lets say from the users table) without clearing the session and the user still has the cookie, because of
if (! is_null($id) && $this->user = $this->provider->retrieveById($id)) { $this->fireAuthenticatedEvent($this->user); }

Every @can directive every Auth check (anything that uses the Auth::user) will cause for a db query spamming the database since the user is never set. On top of that if you do any auth checks in your application with Auth::id() it doesn't return null because of
return $this->user() ? $this->user()->getAuthIdentifier() : $this->session->get($this->getName());

Which is kind of a security issue. Not sure if it is only in my codebase but I thought it would be safer to open this PR to make you aware of the issue!

Thanks for your time

[taylorotwell]

Tests fail.