[php-src] Issue #21070: PHP 8.4.17 RC 1: #71527 Buffer over-write in finfo_open with malformed magic file

Issue: https://github.com/php/php-src/issues/21070
Author: ArchMaster2024

### Description

The following code:

```php
    $finfo = finfo_open(FILEINFO_NONE, __DIR__ . DIRECTORY_SEPARATOR . "bug71527私はガラスを食べられます.magic");
    var_dump($finfo);
<?php
```

Resulted in this output:
```
Warning: finfo_open(/test_php/source/php/ext/fileinfo/tests/bug71527私はガラスを食べられます.magic): Failed to open stream: No such file or directory in /test_php/source/php/ext/fileinfo/tests/bug71527-mb.php on line 2

Warning: finfo_open(/test_php/source/php/ext/fileinfo/tests/bug71527私はガラスを食べられます.magic): Failed to open stream: No such file or directory in /test_php/source/php/ext/fileinfo/tests/bug71527-mb.php on line 2

Warning: finfo_open(): Failed to load magic database at "/test_php/source/php/ext/fileinfo/tests/bug71527私はガラスを食べられます.magic" in /test_php/source/php/ext/fileinfo/tests/bug71527-mb.php on line 2
bool(false)
```

But I expected this output instead:
```
Warning: finfo_open(): Failed to load magic database at "%sbug71527私はガラスを食べられます.magic" in %sbug71527-mb.php on line %d
bool(false)
```


### PHP Version

```plain
PHP 8.4.17RC1 (cli) (built: Jan 25 2026 21:18:17) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.17RC1, Copyright (c) Zend Technologies
```

### Operating System

Debian GNU/Linux 12 (bookworm) x86_64 (container run with podman)