[php-src] Issue #22527: Unterminated JSON strings are misleadingly reported as “Control character error”

Issue: https://github.com/php/php-src/issues/22527
Author: TimWolla

### Description

The following code:

```php
<?php

var_dump(json_decode('"'), json_last_error_msg());
```

Resulted in this output:
```
NULL
string(53) "Control character error, possibly incorrectly encoded"
```

But I expected this output instead: Something about EOF being reached.


### PHP Version

```plain
PHP 8.5.7 (cli) (built: Jun  6 2026 05:36:56) (NTS)
Copyright (c) The PHP Group
Built by Ubuntu
Zend Engine v4.5.7, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.7, Copyright (c), by Zend Technologies
```

### Operating System

_No response_