fix(editor): Add length check for selecting added nodes (no-changelog)

[alexgrozav]

Summary

If adding nodes fails or the node limit is reached, addedNodes will be an empty array.

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/CAT-385/typeerror-cannot-read-properties-of-undefined-reading-id

Review / Merge checklist

• [x] PR title and summary are descriptive. (conventions)
• [ ] Docs updated or follow-up ticket created.
• [ ] Tests included.
• [ ] PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)