meeting.import seemingly can't handle users with `forwarding_committee_ids` set

[luisa-beerboom]

If the json data for a meeting contains users like this one:
"791":{
"poll_voted_ids":[],
"can_change_own_password":true,
"is_physical_person":false,
"is_active":true,
"organization_id":1,
"default_password":"xyz",
"forwarding_committee_ids":[4],
"committee_ids":[3],
"meeting_user_ids":[67],
"vote_ids":[],
"default_vote_weight":"1.000000",
"id":791,
"delegated_vote_ids":[],
"is_present_in_meeting_ids":null,
"meeting_ids":[11],
"option_ids":[],
"poll_candidate_ids":[],
"last_name":"xyz",
"username":"xyz"
"password":"xyz",
}

It seem the import will fail stating the fact, that "forwarding_committee_ids" was set, to be the problem.
We should look into that