Fix/null error in useLanguage

[bjosttveit]

Description

It was somehow possible for language to be used with DatamodelsProvider provided (not ContextNotProvided) but still before they had finished loading (value was null). So adding a null coalecence to return empty array in those cases for the public hooks. But this means they cannot be used to determine loading, but the LoadingBlocker uses the state directly so it should still work as before.

Related Issue(s)

• https://altinn.slack.com/archives/C02EJ9HKQA3/p1729515603349109?thread_ts=1729512254.943649&cid=C02EJ9HKQA3

Verification/QA

• Manual functionality testing
  • I have tested these changes manually
  • Creator of the original issue (or service owner) has been contacted for manual testing (or will be contacted when released in alpha)
  • No testing done/necessary
• Automated tests
  • Unit test(s) have been added/updated
  • Cypress E2E test(s) have been added/updated
  • No automatic tests are needed here (no functional changes/additions)
  • I want someone to help me make some tests
• UU/WCAG (follow these guidelines until we have our own)
  • I have tested with a screen reader/keyboard navigation/automated wcag validator
  • No testing done/necessary (no DOM/visual changes)
  • I want someone to help me perform accessibility testing
• User documentation @ altinn-studio-docs
  • Has been added/updated
  • No functionality has been changed/added, so no documentation is needed
  • I will do that later/have created an issue
• Support in Altinn Studio
  • Issue(s) created for support in Studio
  • This change/feature does not require any changes to Altinn Studio
• Sprint board
  • The original issue (or this PR itself) has been added to the Team Apps project and to the current sprint board
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• Labels
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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
87.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud