fix: UserModel::assignIdentities() always produces a DB query

[michalsn]

In the UserModel - when we use withIdentities() method the query is produced properly.

The problem occurs in the assignIdentities() method, when we're trying to assign identities to the users.
We're working with the User entity, and there is a line:

$newIdentities   = $mappedUsers[$userId]->identities;

It will call getIdentities() method which will produce a query to the DB, since there are no identities assigned yet.

This PR solves this problem.

[datamweb]

@michalsn thank you!

[kenjis]

Am I correct in assuming that this PR prevents queries to retrieve unnecessary Identities from being executed?
It's just useless and there has never been a problem with the results returned.

[kenjis]

The code looks good.

[michalsn]

Am I correct in assuming that this PR prevents queries to retrieve unnecessary Identities from being executed?
It's just useless and there has never been a problem with the results returned.

There was never a problem with the incorrect result per se. The problem here was that we were producing n+1 queries for code like this:

$users = model(UserModel::class)->withIdentities()->findAll();
foreach ($users as $user) {
    $user->email;
}

That would be just fine, but since we use withIdentities() it should not work that way.

[datamweb]

Thanks All!