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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.52%. Comparing base (05194d8) to head (13c7a4a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3927   +/-   ##
=======================================
  Coverage   94.52%   94.52%           
=======================================
  Files         313      313           
  Lines       14767    14770    +3     
  Branches     2496     2495    -1     
=======================================
+ Hits        13958    13962    +4     
+ Misses        804      803    -1     
  Partials        5        5           

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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