undefined _observer in c-table disconnectedCallback

[juholehtocsc]

Happens rarely, but still happens.

The component throws in disconnectedCallback because _observer is not always initialized before teardown.

Affected version
@cscfi/csc-ui 3.0.19

Error
TypeError: Cannot read properties of undefined (reading 'disconnect')
at Lt.disconnectedCallback (c-table.tsx:114:20)

this._observer.disconnect();
without a null guard.
The same package appears to use null-safe teardown in other components (for example c-data-table uses optional chaining), so this looks inconsistent.