Resolve TROVE-2020-004

This is a remotely triggerable memory leak on relays and clients, found by tobias pulls.

The issue is that when circpad_setup_machine_on_circ() is reached with an inconsistent internal configuration, it fails to free an object that is replaced. It logs a bug warning, but that isn't enough.

Tobias Pulls found that this code was actually reachable, though, and results in a memory leak.