message: fix http call response crash
diff: @@ -1759,7 +1759,8 @@ void Context::setEncoderFilterCallbacks(Envoy::Http::StreamEncoderFilterCallback
  void Context::onHttpCallSuccess(uint32_t token, Envoy::Http::ResponseMessagePtr& response) {
  http_call_response_ = &response;
  - onHttpCallResponse(token, response->headers().size(), response->body()->length(),
  + uint32_t body_size = response->body() ? response->body()->length() : 0;
  + onHttpCallResponse(token, response->headers().size(), body_size,
  headerSize(response->trailers()));
  http_call_response_ = nullptr;
  http_request_.erase(token);
  