### Elasticsearch Version

main

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

Darwin

### Problem Description

Sorting fails sometimes with the error

```
No TopN sorting encoder for type UNSUPPORTED
```


### Steps to Reproduce

Playing with ES|QL I tried to run the following query

`from logstash-* | sort extension.keyword`

This returns the error

```
No TopN sorting encoder for type UNSUPPORTED
```

If I run the query:

`from logstash-*  | keep extension.keyword | sort extension.keyword`

the data return successfully.

### Logs (if relevant)

_No response_
x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/lucene/ValueSources.java
public static final String MATCH_ONLY_TEXT = "match_only_text";
    private ValueSources() {}
    public static List<ValueSourceInfo> sources(
        List<SearchContext> searchContexts,
        String fieldName,
        boolean asUnsupportedSource,
        ElementType elementType
    ) {
        List<ValueSourceInfo> sources = new ArrayList<>(searchContexts.size());
        for (SearchContext searchContext : searchContexts) {
            
            
            
            ShardSearchRequest shardRequest = searchContext.request();
            SearchExecutionContext ctx = searchContext.readerContext()
                .indexService()
                .newSearchExecutionContext(
                    shardRequest.shardId().id(),
                    shardRequest.shardRequestIndex(),
                    searchContext.searcher(),
                    shardRequest::nowInMillis,
                    shardRequest.getClusterAlias(),
                    shardRequest.getRuntimeMappings()
                );
            var fieldType = ctx.getFieldType(fieldName);
            if (fieldType == null) {
                sources.add(new ValueSourceInfo(new NullValueSourceType(), new NullValueSource(), elementType, ctx.getIndexReader()));
                continue;