Prefill of foreign business address does not include postal city

## Describe the bug

## To Reproduce
Steps to reproduce the behavior:

We have the following prefill json
```
{
"$schema": "https://altinncdn.no/schemas/json/prefill/prefill.schema.v1.json",
"allowOverwrite": true,
"ER": {
"OrgNumber": "Virksomhet.Organisasjonsnummer",
"Name": "Virksomhet.Navn",
"UnitType": "Virksomhet.Organisasjonsform",
"BusinessAddress": "Virksomhet.Adresse.Gateadresse",
"BusinessPostalCode": "Virksomhet.Adresse.Postnr",
"BusinessPostalCity": "Virksomhet.Adresse.Poststed"
},
"DSF": {
},
"UserProfile": {
}
}
```

When opening a company with a foreign business address with no postal code, but still a postal city in brreg, it does not include the postal city as I would expect when prefilling.

## Expected behavior

Prefill should include postal city

## Screenshots
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## Additional info
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App: dat/innkvartering

Start by tracing the prefill handling for ER.BusinessPostalCity and reproduce the issue with the provided JSON using a foreign business address that has a postal city but no postal code. Done means the postal city is included when the form is opened, even when the postal code is absent.

Written by the indexing model from the issue text.