Fix node availability when propagating import copy

[vkWeb]

Summary

Here I've fixed the undefined original_source_node_id TypeError. After importing a contentnode, when this change was getting relayed to the other channel editor, we were getting that error on the other channel editor's end because the contentnode which has to be imported was not present in the Indexed DB.

Investigation credits to our ironman @bjester. Code credits to me.

Manual verification steps performed

1. Login as a@a.com (admin).
2. Create a new channel with any resource, for e.g. one PDF file. Publish it and make it public.
3. Create another channel.
4. Invite user@b.com to this new channel with edit rights.
5. On another browser window login as user@b.com, accept the invitation and open the invited channel.
6. From admin browser, import a content from the public channel.
7. Check the user@b.com browser, the imported content should be visible.
8. There must be no error on the developer console.

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Reviewer guidance

Manual verification steps should be enough.

References

Closes #4332.

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Contributor's Checklist

PR process:

• If this is an important user-facing change, PR or related issue the CHANGELOG label been added to this PR. Note: items with this label will be added to the CHANGELOG at a later time
• If this includes an internal dependency change, a link to the diff is provided
• The docs label has been added if this introduces a change that needs to be updated in the user docs?
• If any Python requirements have changed, the updated requirements.txt files also included in this PR
• Opportunities for using Google Analytics here are noted
• Migrations are safe for a large db

Studio-specifc:

• All user-facing strings are translated properly
• The notranslate class been added to elements that shouldn't be translated by Google Chrome's automatic translation feature (e.g. icons, user-generated text)
• All UI components are LTR and RTL compliant
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Testing:

• Code is clean and well-commented
• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Any new interactions have been added to the QA Sheet
• Critical and brittle code paths are covered by unit tests

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Reviewer's Checklist

This section is for reviewers to fill out.

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[bjester]

This looks like the right change to me. Since this occurs in handling remote changes, this is unlikely to break anything, but we will test this during pre-release QA.