lost watch when client send two request without nonce

log

```
[2022-04-25 19:13:25.993] [DEBUG] [grpc-default-executor-0] [i.e.controlplane.server.OspDiscoveryServer] >>> [0] open stream from
[2022-04-25 19:13:26.009] [DEBUG] [grpc-default-executor-0] [i.e.controlplane.server.OspDiscoveryServer] >>> [0] request type.googleapis.com/envoy.api.v2.ClusterLoadAssignment[r1] with nonce from version 3
[2022-04-25 19:13:26.684] [DEBUG] [grpc-default-executor-0] [i.e.controlplane.server.OspDiscoveryServer] >>> [0] response type.googleapis.com/envoy.api.v2.ClusterLoadAssignment with nonce 0 version 0
[2022-04-25 19:13:26.696] [DEBUG] [grpc-default-executor-0] [i.e.controlplane.server.OspDiscoveryServer] >>> [0] request type.googleapis.com/envoy.api.v2.ClusterLoadAssignment[r1, r2, r3, r4] with nonce from version 3
```

When I restart xds server, C++ client will send two request without nonce for one resourceType, xds server response first request, then handle the second request.

In the code, xds server will discard the second request, watch resources in second request will lost.

```
LatestDiscoveryResponse latestDiscoveryResponse = latestResponse(requestTypeUrl);
String resourceNonce = latestDiscoveryResponse == null ? null : latestDiscoveryResponse.nonce();

if (isNullOrEmpty(resourceNonce) || resourceNonce.equals(nonce)) {
if (!request.hasErrorDetail() && latestDiscoveryResponse != null) {
setAckedResources(requestTypeUrl, latestDiscoveryResponse.resourceNames());
}

computeWatch(requestTypeUrl, () -> discoveryServer.configWatcher.createWatch(
ads(),
request,
ackedResources(requestTypeUrl),
r -> executor.execute(() -> send(r, requestTypeUrl)),
hasClusterChanged
));
}
```