### 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, numOps, null);
                }
                ++numOps;
            }
            
            for (String clusterAlias : remoteClusterIndices.keySet()) {
                performRemoteClusterOperation(clusterAlias, remoteClusterIndices.get(clusterAlias), numOps);
                ++numOps;
            }
        }
        
        boolean checkForEarlyFinish() {
            long now = System.currentTimeMillis();
            if ((now - task.getStartTime()) > request.timeout().getMillis()) {
                finishHim(false);
                return true;
            }
            return false;
        }
        protected void performOperation(final String nodeId, final Set<ShardId> shardIds, final int opsIndex) {
            if (shardIds.size() == 0) {
                
                onNodeFailure(nodeId, opsIndex, null);
            } else {
                try {
                    final NodeTermsEnumRequest nodeRequest = newNodeRequest(localIndices, nodeId, shardIds, request, task.getStartTime());
                    nodeRequest.setParentTask(clusterService.localNode().getId(), task.getId());
                    DiscoveryNode node = nodes.get(nodeId);
                    if (node == null) {