[php-src] Issue #23447: segfault on soap server handler when it contains undefined constant

Issue: https://github.com/php/php-src/issues/23447
Author: lmaltsis

### Description

The following code:

```php
<?php
class foo { private $broken = undefinedConstant; }
$server = new SoapServer(null, array('uri' => ''));
$server->setClass('foo');
$server->handle(<<<'XML'
<?xml version="1.0"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
  <SOAP-ENV:Body><anything/></SOAP-ENV:Body>
</SOAP-ENV:Envelope>
XML);
```

Resulted in this output:
```
Segmentation fault (core dumped)
```

But I expected this output instead:
``undefined constant error``


### PHP Version

```plain
PHP 8.5.9 (cli) (built: Aug  7 2026 18:15:17) (NTS DEBUG)
Copyright (c) The PHP Group
Zend Engine v4.5.9, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.9, Copyright (c), by Zend Technologies
```

### Operating System

Ubuntu 24.04