Fix error that occurs if facilityDatasetExtraFields is null.

[rtibbles]

Summary

• Prevents property access on null or undefined for facilityDatasetExtraFields

References

Fixes https://github.com/learningequality/kolibri/issues/12533

Reviewer guidance

Make sure that you can still load the demographic editing in the user editing in the admin UI.

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Testing checklist

• [ ] 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
• [ ] Critical and brittle code paths are covered by unit tests

PR process

• [ ] PR has the correct target branch and milestone
• [ ] PR has 'needs review' or 'work-in-progress' label
• [ ] If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• [ ] If this is an important user-facing change, PR or related issue has a 'changelog' label
• [ ] If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• 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

[github-actions[bot]]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.17.0rc2.dev0_git.2.gf683a154.pex
Windows Installer (EXE)	kolibri-0.17.0rc2.dev0+git.2.gf683a154-windows-setup-unsigned.exe
Debian Package	kolibri_0.17.0rc2.dev0+git.2.gf683a154-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.17.0rc2.dev0+git.2.gf683a154.dmg
Android Package (APK)	kolibri-0.17.0rc2.dev0+git.2.gf683a154-0.1.4-debug.apk
TAR file	kolibri-0.17.0rc2.dev0+git.2.gf683a154.tar.gz
WHL file	kolibri-0.17.0rc2.dev0+git.2.gf683a154-py2.py3-none-any.whl

[radinamatic]

Tested user creation (all types), user properties editing, user deletion, class assignment, both on the original and one newly created additional facility. All is 🟢 to go! 👏🏽 🚀