ReplicationCoordinatorImpl::_cancelElectionIfNeeded_inlock() assumes a candidate always has a _voteRequester, which isn't true for stepup command that skips dry run.

Stepup command due to election handoff skips dry run and writes down the vote for itself after changing its role to kCandidate, then releases the mutex. Another thread calling _cancelElectionIfNeeded_inlock() will hit the invariant if it runs in this window until the node finishes the write and starts _voteRequester.