message: config: delta RDS: don't onConfigUpdate when no resources
  Previously, an empty update was passed through to state-of-the-world onConfigUpdate, with system_version_info as the version.
  Risk Level: low
diff: @@ -129,8 +129,7 @@ void RdsRouteConfigSubscription::onConfigUpdate(
  void RdsRouteConfigSubscription::onConfigUpdate(
  const Protobuf::RepeatedPtrField<envoy::api::v2::Resource>& added_resources,
  - const Protobuf::RepeatedPtrField<std::string>& removed_resources,
  - const std::string& system_version_info) {
  + const Protobuf::RepeatedPtrField<std::string>& removed_resources, const std::string&) {
  if (!removed_resources.empty()) {
  // TODO(#2500) when on-demand resource loading is supported, an RDS removal may make sense (see
  // discussion in #6879), and so we should do something other than ignoring here.
  @@ -139,13 +138,10 @@ void RdsRouteConfigSubscription::onConfigUpdate(
  "Server sent a delta RDS update attempting to remove a resource (name: {}). Ignoring.",
  removed_resources[0]);
  }
  - Protobuf::RepeatedPtrField<ProtobufWkt::Any> unwrapped_resource;
  if (!added_resources.empty()) {
  + Protobuf::RepeatedPtrField<ProtobufWkt::Any> unwrapped_resource;
  *unwrapped_resource.Add() = added_resources[0].resource();
  onConfigUpdate(unwrapped_resource, added_resources[0].version());
  - } else {
  - onConfigUpdate({}, system_version_info);
  - return;
  }
  }
  