### Elasticsearch Version

8.3.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

arm64

### Problem Description

When using the `_terms_enum` API, if remote clusters return failures, but the local cluster doesn't, a null exception is thrown:

```
{
  "error": {
    "root_cause": [
      {
        "type": "null_pointer_exception",
        "reason": "Cannot invoke \"java.util.List.add(Object)\" because \"shardFailures\" is null"
      }
    ],
    "type": "null_pointer_exception",
    "reason": "Cannot invoke \"java.util.List.add(Object)\" because \"shardFailures\" is null"
  },
  "status": 500
}
```

### Steps to Reproduce

Call the _terms_enum API with a remote cluster that will return failures, e.g. because of this bug: https://github.com/elastic/elasticsearch/issues/86187

### Logs (if relevant)

_No response_
x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/termsenum/action/TransportTermsEnumAction.java
onNodeFailure(nodeId, opsIndex, null);
                    } else if (checkForEarlyFinish() == false) {
                        transportService.sendRequest(
                            node,
                            transportShardAction,
                            nodeRequest,
                            new TransportResponseHandler<NodeTermsEnumResponse>() {
                                @Override
                                public NodeTermsEnumResponse read(StreamInput in) throws IOException {
                                    return readShardResponse(in);
                                }
                                @Override
                                public void handleResponse(NodeTermsEnumResponse response) {
                                    onNodeResponse(nodeId, opsIndex, response);
                                }
                                @Override
                                public void handleException(TransportException exc) {
                                    onNodeFailure(nodeId, opsIndex, exc);
                                }
                            }
                        );
                    }
                } catch (Exception exc) {
                    onNodeFailure(nodeId, opsIndex, exc);
                }
            }
        }
        void performRemoteClusterOperation(final String clusterAlias, final OriginalIndices remoteIndices, final int opsIndex) {
            try {
                TermsEnumRequest req = new TermsEnumRequest(request).indices(remoteIndices.indices());