### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

all

### Problem Description

Do this

### Steps to Reproduce

```
rm /tmp/evil
for a in {0..9}; do
   for b in {0..9}; do
      echo '{"index": {}}' >> /tmp/evil
      echo '{"a": '$a', "b": '$b'}' >> /tmp/evil
   done
done
echo >> /tmp/evil

curl -uelastic:password -XDELETE localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPUT localhost:9200/test
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_bulk --data-binary @/tmp/evil
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_forcemerge?max_num_segments=1
curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/test/_refresh

curl -HContent-Type:application/json -uelastic:password -XPOST localhost:9200/_esql?pretty -d'{
   "query": "FROM test | STATS MAX(a) BY a, b | KEEP a"
}'
```

### Logs (if relevant)

_No response_
x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/AggregationOperator.java
}
        output = new Page(blocks);
    }
    @Override
    public boolean isFinished() {
        return finished && output == null;
    }
    @Override
    public void close() {
        Releasables.close(aggregators);
    }
    private static void checkState(boolean condition, String msg) {
        if (condition == false) {
            throw new IllegalArgumentException(msg);
        }
    }
    private static void checkNonEmpty(List<?> list) {
        if (list.size() < 1) {
            throw new IllegalArgumentException("empty list");
        }
    }
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(this.getClass().getSimpleName()).append("[");
        sb.append("aggregators=").append(aggregators).append("]");
        return sb.toString();
    }
}