### Elasticsearch Version

8.8.2

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

Mac OS X

### Problem Description

Under certain conditions, fetching a particular field value using the "fields" API can lead to `string_index_out_of_bounds_exception`.
The queried field needs to be inside a "nested" object and in addition to the field name, all fields need to be queries as well (`*`).
Both fields requested also need to be requested with `"include_unmapped": true`. 

### Steps to Reproduce

```
DELETE testindex

PUT testindex
{
    "mappings": {
        "dynamic": "false",
        "properties": {
            "nested_field": {
                "type": "nested",
                "properties": {
                    "file": {
                        "type": "keyword"
                    }
                }
            }
        }
    }
}

POST testindex/_doc
{
    "nested_field": {        
            "file": "somefile.txt"
    }
}

GET testindex/_search
{
  "_source": false,
  "fields": [
    {
      "field": "file",
      "include_unmapped": true
    },
    {
      "field": "*",
      "include_unmapped": true
    }
  ],
  "query": {
    "match_all" : {}
  }
}
```

This gives the following error:
```
{
    "error": {
        [...],
        "caused_by": {
            "type": "string_index_out_of_bounds_exception",
            "reason": "Range [13, 4) out of bounds for length 4",
            "caused_by": {
                "type": "string_index_out_of_bounds_exception",
                "reason": "Range [13, 4) out of bounds for length 4"
            }
        }
    },
    "status": 500
}
```

### Logs (if relevant)

_No response_
server/src/test/java/org/elasticsearch/search/fetch/subphase/FieldFetcherTests.java
assertThat(dateField.getValues().size(), equalTo(1));
        assertThat(dateField.getValue(), equalTo("1990/12/29"));
        
        source = XContentFactory.jsonBuilder()
            .startObject()
            .field("field", "value")
            .array("date_field", "1990-12-29T00:00:00.000Z", "baddate", "1991-12-29T00:00:00.000Z")
            .endObject();
        DocumentField dates = fetchFields(mapperService, source, List.of(new FieldAndFormat("date_field", "yyyy/MM/dd"))).get("date_field");
        assertThat(dates.getValues().size(), equalTo(2));
        assertThat(dates, containsInAnyOrder(equalTo("1990/12/29"), equalTo("1991/12/29")));
    }
    public void testIgnoreAbove() throws IOException {
        MapperService mapperService = createMapperService(fieldMapping(b -> {
            b.field("type", "keyword");
            b.field("ignore_above", 20);
        }));
        XContentBuilder source = XContentFactory.jsonBuilder()
            .startObject()
            .array("field", "value", "other_value", "really_really_long_value")
            .endObject();
        Map<String, DocumentField> fields = fetchFields(mapperService, source, "field");
        DocumentField field = fields.get("field");
        assertThat(field.getValues().size(), equalTo(2));
        source = XContentFactory.jsonBuilder().startObject().array("field", "really_really_long_value").endObject();
        fields = fetchFields(mapperService, source, "field");
        assertThat(fields.get("field").getValues().size(), equalTo(0));
        assertThat(fields.get("field").getIgnoredValues().size(), equalTo(1));
    }
    public void testFieldAliases() throws IOException {