use empty array for layouts if not yet loaded when changing layoutset

[standeren]

Description

Related Issue(s)

• #{issue number}

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• Cypress tests run green locally (https://github.com/Altinn/altinn-studio/tree/master/frontend/testing/cypress#run-altinn-studio-tests)

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (d69852b) 82.82% compared to head (524c97f) 82.86%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11340      +/-   ##
==========================================
+ Coverage   82.82%   82.86%   +0.03%     
==========================================
  Files         838      840       +2     
  Lines       12626    12626              
  Branches     1691     1689       -2     
==========================================
+ Hits        10458    10463       +5     
+ Misses       1906     1901       -5     
  Partials      262      262              

Files	Coverage Δ
...tend/packages/shared/src/hooks/useEventListener.ts	100.00% <100.00%> (ø)
...ntend/packages/shared/src/hooks/useLocalStorage.ts	100.00% <100.00%> (ø)
.../shared/src/providers/PreviewConnectionContext.tsx	88.23% <100.00%> (ø)
frontend/packages/shared/src/utils/webStorage.ts	78.57% <ø> (ø)
frontend/packages/ux-editor/src/AppContext.ts	100.00% <100.00%> (ø)
frontend/packages/ux-editor/src/SubApp.tsx	100.00% <100.00%> (ø)
...or/src/components/Elements/LayoutSetsContainer.tsx	95.00% <100.00%> (-5.00%)	⬇️
...tor/src/components/FormComponent/FormComponent.tsx	95.12% <100.00%> (-0.12%)	⬇️
...kages/ux-editor/src/components/Preview/Preview.tsx	86.36% <100.00%> (ø)
...editor/src/components/config/EditFormContainer.tsx	73.07% <100.00%> (+0.34%)	⬆️
... and 17 more

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[TomasEng]

Mye bra opprydning her! Det hadde vært fint om vi kunne laget en test på event-lytteren. Dette er en algoritme som vi bruker flere steder, så jeg forslår at vi gjør det til en egen hook, som i designsystemet: https://github.com/digdir/designsystem/blob/main/packages/react/src/hooks/useEventListener.ts

[TomasEng]

Veldig bra! Får du kjørt Cypress-testene lokalt? Det er endringer i mange filer her, så det hadde vært fint å verifisere at det ikke brekker noe.
Enhetstester har du fikset så langt det lar seg gjøre, så punktet om automatisert test kan du krysse av for 🙂