Prevent MutationObserver error when removedNodes is empty

[MOBermejo]

This PR fixes a bug on the faction page that caused an error when removedNodes was empty.

The MutationObserver listens for changes to the faction member list, but if removedNodes is an empty NodeList, it triggered the following error: Cannot read properties of undefined (reading 'matches')

• Added optional chaining (?.) to prevent the script from calling .matches() on undefined.
• Ensures the observer safely continues when removedNodes exists, but is empty

[DeKleineKobini]

Any changes should be added in the extension/changelog.json file under the first unreleased version.
First contributions should also update extension/ scripts/global/team.js to add yourself as member and choose a color for in the changelog.

CONTRIBUTING.md

Other than that, it will do as a temporary fix. Created #837 for a more permanent fix which wouldn't break as easily when Torn changes anything.