[php-src] Issue #21193: Previous `create_sid` handler remains active when not explicitly overridden

Issue: https://github.com/php/php-src/issues/21193
Author: TimWolla

### Description

The following code:

```php
<?php

ob_start();

session_set_save_handler(
	function ($savePath, $sessionName) {
		var_dump("open");

		return true;
	},
	function () {
		var_dump("close");

		return true;
	},
	function ($id) {
		var_dump("read");

		return '';
	},
	function ($id, $data) {
		var_dump("write");

		return true;
	},
	function ($id) {
		var_dump("destroy");

		return true;
	},
	function ($maxlifetime) {
		var_dump("gc");

		return true;
	},
	function () {
		var_dump("create_sid");

		return 'foo';
	}
);

session_set_save_handler(
	function ($savePath, $sessionName) {
		var_dump("open");

		return true;
	},
	function () {
		var_dump("close");

		return true;
	},
	function ($id) {
		var_dump("read");

		return '';
	},
	function ($id, $data) {
		var_dump("write");

		return true;
	},
	function ($id) {
		var_dump("destroy");

		return true;
	},
	function ($maxlifetime) {
		var_dump("gc");

		return true;
	},
);

session_start();
```

Resulted in this output:
```
string(4) "open"
string(10) "create_sid"
string(4) "read"
string(5) "write"
string(5) "close"
```

But I expected this output instead:
```
string(4) "open"
string(4) "read"
string(5) "write"
string(5) "close"
```


### PHP Version

```plain
PHP 8.4.17 (cli) (built: Jan 18 2026 14:19:44) (NTS)
Copyright (c) The PHP Group
Built by Debian
Zend Engine v4.4.17, Copyright (c) Zend Technologies
    with Zend OPcache v8.4.17, Copyright (c), by Zend Technologies
```

### Operating System

_No response_