Fixed issue where getRoles and getPermissions methods returned empty lists

[konovalov-nk]

This fixes issue on Laravel 5.3 where existing model instances wouldn't work:

$user_admin = \App\User::first();
$user_admin->assignRole(ROLE_ADMIN);

// $user_admin->getRoles is empty!
$this->assertEquals($user_admin->getRoles(), [
    1 => ROLE_ADMIN
]);
// $user_admin->getPermissions is empty!
$this->assertEquals($user_admin->getPermissions(), $admin_role->getPermissions());

However, new created user works:

$user_admin = new User();
$user_admin->firstname = 'Role';
$user_admin->lastname = 'test';
$user_admin->newsletter = 0;
$user_admin->email = '[email protected]';
$user_admin->password = 'RoleTest';
$user_admin->save();

$user_admin->assignRole(ROLE_ADMIN);

// Test passes.
$this->assertEquals($user_admin->getRoles(), [
    1 => ROLE_ADMIN
]);
// Test passes.
$this->assertEquals($user_admin->getPermissions(), $admin_role->getPermissions());