message: [security] remove panic from from_proto function
  This paths should be reachable as the field is optional. I don't think we should have panics in `from_proto` functions.
diff: @@ -420,7 +420,7 @@ impl FromProto for RequestItem {
  fetch_events,
  }
  } else {
  - unreachable!("Unknown RequestItem type.")
  + bail!("Unknown RequestItem type.")
  })
  }
  }
  @@ -608,7 +608,7 @@ impl FromProto for ResponseItem {
  txn_list_with_proof,
  }
  } else {
  - unreachable!("Unknown ResponseItem type.")
  + bail!("Unknown ResponseItem type.")
  })
  }
  }
  