Empty cycle point - `getFamilyTree()` TypeError

[MetRonnie]

Description

I had a workflow open with the tree view. I uninstalled, reinstalled, and started it.

Uncaught TypeError: Cannot read properties of undefined (reading 'slice')

Location: https://github.com/cylc/cylc-ui/blob/b0204f2d7d2d4848bd5f6d7ec9972f4ef23fc691/src/store/workflows.module.js#L322

node has no property ancestors.

It caused a cycle point to show up as empty, similar to in #1813