fix:mirador_crash

[fstoe]

I found out that adding something through the add button in the catalog view which is json but not a manifest makes the viewer crash.
steps to reproduce:

• Open Mirador
• Add Resource with example url: https://iiif.io/api/presentation/2/context.json
• Open legit resource

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.40%. Comparing base (3c87395) to head (3f2a803).
Report is 8 commits behind head on master.

Files	Patch %	Lines
src/state/selectors/manifests.js	60.00%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3927      +/-   ##
==========================================
- Coverage   92.43%   92.40%   -0.03%     
==========================================
  Files         203      203              
  Lines        3581     3583       +2     
==========================================
+ Hits         3310     3311       +1     
- Misses        271      272       +1     

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[lutzhelm]

Hi @fstoe, could you add a test case for that patch? createManifestoInstance itself is not exported, but getManifestoInstance calls it directly, so this would be a good place to add a test:

https://github.com/ProjectMirador/mirador/blob/master/__tests__/src/selectors/manifests.test.js#L56-L68

Something like

it('does not crash if json is not a manifest', () => {
  const state = { manifests: { x: { json: {} } } };
  const received = getManifestoInstance(state, { manifestId: 'x' });
  expect(received).toBe(undefined);
});

[fstoe]

Hey @lutzhelm,
thanks for the comment. I just added a small test case