[php-src] Issue #20815: PHP 8.3 with libcurl 7.29.0 segmentation fault

Issue: https://github.com/php/php-src/issues/20815
Author: thg2k

### Description

I know this is a bit late to the party, but as the last 8.3 bugfix release is about to happen, I was wondering if we can get this segfault fixed.

The reason is very straightforward, the multi init should be followed by at least one curl_multi_add_handler before it is destroyed, otherwise the library crashes in the curl_multi_cleanup function.

I'd happy to provide a PR but I will need a few more days, if somebody has a quick fix idea please go ahead.

For the records, this bug exists since at least PHP 7.2.

The following code:

```php
<?php
$ch = curl_multi_init();
unset($ch);
print "EOF\n";
```

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

But I expected this output instead:
```
EOF
```


### PHP Version

```plain
PHP 8.3.29 (cli) (built: Dec 29 2025 17:10:47) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.29, Copyright (c) Zend Technologies
```

### Operating System

_No response_