avoid errors in JS console from new data menu scrolling logic

[kecnry]

Description

This pull request avoids JS console messages introduced by #2630 by gracefully existing if parentElement is not defined.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[haticekaratay]

Thanks for the fix! Looks good to me!

[codecov]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (fb3cf40) 90.82% compared to head (be38873) 90.81%.
Report is 4 commits behind head on main.

Files	Patch %	Lines
jdaviz/style_registry.py	83.78%	6 Missing ⚠️
jdaviz/utils.py	66.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2707      +/-   ##
==========================================
- Coverage   90.82%   90.81%   -0.02%     
==========================================
  Files         163      164       +1     
  Lines       21503    21572      +69     
==========================================
+ Hits        19530    19590      +60     
- Misses       1973     1982       +9     

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