requestor: fail when a request execution ends with request not finished but not failed either.
The security/protos test fails on crashing on this assert: https://gitlab.labs.nic.cz/labs/knot/blob/master/src/knot/zone/events/handlers.c#L403
The test intentionally sends malformed requests. The fix is to make the corrected if
pass on the same input as it did in 1.6.