message: Only vote if there are options to vote for!
  `ActiveValidator` must not produce ballots if there are no blocks to
  vote for, otherwise the fork choice panics.
diff: @@ -102,9 +102,11 @@ impl<C: Context> ActiveValidator<C> {
  effects.push(Effect::RequestNewBlock(bctx));
  } else if round_offset == self.witness_offset() {
  let panorama = state.panorama_cutoff(state.panorama(), timestamp);
  + if !panorama.is_empty() {
  let witness_vote = self.new_vote(panorama, timestamp, None, state);
  effects.push(Effect::NewVertex(ValidVertex(Vertex::Vote(witness_vote))))
  }
  + }
  effects
  }
  @@ -119,10 +121,12 @@ impl<C: Context> ActiveValidator<C> {
  warn!(%timestamp, "skipping outdated confirmation");
  } else if self.should_send_confirmation(vhash, timestamp, state) {
  let panorama = self.confirmation_panorama(vhash, state);
  + if !panorama.is_empty() {
  let confirmation_vote = self.new_vote(panorama, timestamp, None, state);
  let vv = ValidVertex(Vertex::Vote(confirmation_vote));
  return vec![Effect::NewVertex(vv)];
  }
  + }
  vec![]
  }
  