message: [safety-rules] don't recompute values
  trivial commit to not recompute a value
  Closes:
  Approved by: joshlind
diff: @@ -104,13 +104,14 @@ impl<T: Payload> SafetyRules<T> {
  /// @TODO if public key does not match private key in validator set, access persistent storage
  /// to identify new key
  fn start_new_epoch(&mut self, ledger_info: &LedgerInfo) -> Result<(), Error> {
  - let epoch_info = ledger_info.next_epoch_info().cloned();
  - self.validator_verifier = Some(epoch_info.ok_or(Error::InvalidLedgerInfo)?.verifier);
  -
  + let epoch_info = ledger_info
  + .next_epoch_info()
  + .cloned()
  + .ok_or(Error::InvalidLedgerInfo)?;
  + self.validator_verifier = Some(epoch_info.verifier);
  let current_epoch = self.persistent_storage.epoch()?;
  - let next_epoch = ledger_info.epoch() + 1;
  - if current_epoch < next_epoch {
  + if current_epoch < epoch_info.epoch {
  // This is ordered specifically to avoid configuration issues:
  // * First set the waypoint to lock in the minimum restarting point,
  // * set the round information,
  @@ -120,7 +121,7 @@ impl<T: Payload> SafetyRules<T> {
  .set_waypoint(&Waypoint::new_epoch_boundary(ledger_info)?)?;
  self.persistent_storage.set_last_voted_round(0)?;
  self.persistent_storage.set_preferred_round(0)?;
  - self.persistent_storage.set_epoch(ledger_info.epoch() + 1)?;
  + self.persistent_storage.set_epoch(epoch_info.epoch)?;
  }
  Ok(())
  