Fix display of cycle points that don't have children in tree view

[MetRonnie]

Partially addresses #1999 by fixing the display, but does not fix the cause of the issue.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Tests are not needed
• Changelog entry included if this is a change that can affect users
• No docs needed
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

This isn't a display issue, it's a problem with the data in the UI store and a memory leak. We should fix the issue rather than trying to cover it over in this way.

[MetRonnie]

This is not covering anything up, it's just aiming to fix the display aspect of the issue. However I've realised it still leaves the expand/collapse button visible and it would be tricky to include that, so I'll just pull out the tidying into a new PR