FIX: Fixed "MissingReferenceException" errors when closing an in-game dropdown field

[bmalrat]

Description

When closing a dropdown field the ui module still reference a deleted object and try to use it with a null propagation operator which is not compatible with unity object https://github.com/microsoft/Microsoft.Unity.Analyzers/blob/main/doc/UNT0008.md

Changes made

Changed the access to use the bool operator check

Testing

tested with customer project

Risk

Please describe the potential risks of your changes for the reviewers.

Checklist

Before review:

• [ X] Changelog entry added.
  • Explains the change in Changed, Fixed, Added sections.
  • For API change contains an example snippet and/or migration example.
  • JIRA ticket linked, example (case %%). If it is a private issue, just add the case ID without a link.
  • Jira port for the next release set as "Resolved".
• Tests added/changed, if applicable.
  • Functional tests Area_CanDoX, Area_CanDoX_EvenIfYIsTheCase, Area_WhenIDoX_AndYHappens_ThisIsTheResult.
  • Performance tests.
  • Integration tests.
• Docs for new/changed API's.
  • Xmldoc cross references are set correctly.
  • Added explanation how the API works.
  • Usage code examples added.
  • The manual is updated, if needed.

During merge:

• Commit message for squash-merge is prefixed with one of the list:
  • NEW: ___.
  • FIX: ___.
  • DOCS: ___.
  • CHANGE: ___.
  • RELEASE: 1.1.0-preview.3.

After merge:

• Create forward/backward port if needed. If you are blocked from creating a forward port now please add a task to ISX-1444.

[benoitalain]

Thank you!

[lyndon-unity]

Looks good - thank you.

[kamyker]

Thanks, couldn't use Unity 6 without this fix (upgraded from 2022).