fix(chatroom): guard against undefined values to avoid crashes

[Alok-work23]

Description

This PR adds null-safety guards in ChatRoom to prevent potential runtime errors when optional values are undefined.

Related Issue

N/A – This PR addresses a potential runtime issue identified during code review.

Motivation and Context

Both participantPropertyListener and node.children are optional and may be undefined in certain scenarios.
This PR ensures safer handling of these cases and improves overall robustness.

How Has This Been Tested?

N/A

Screenshots or GIF (In case of UI changes): N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[jitsi-jenkins]

Hi, thanks for your contribution!
If you haven't already done so, could you please make sure you sign our CLA (https://jitsi.org/icla for individuals and https://jitsi.org/ccla for corporations)? We would unfortunately be unable to merge your patch unless we have that piece :(.

[Alok-work23]

I have signed CLA.