message: Add check instead of assert
diff: @@ -88,7 +88,7 @@ PacketNumEncodingResult encodeLongHeaderHelper(
  appender.push(originalDstConnId->data(), originalDstConnId->size());
  // Write the retry token
  - assert(token && "token is nullptr");
  + CHECK(token) << "Retry packet must contain a token";
  appender.insert(*token);
  }
  // defer write of the packet num and length till payload has been computed
  