[php-src] Issue #22629: ext/uri: WHATWG Validation error incorrect with empty host and non-empty userinfo

Issue: https://github.com/php/php-src/issues/22629
Author: JKingweb

### Description

The following code:

```php
<?php
try {
    new Uri\WhatWg\Url("https://user:pass@");
} catch (Throwable $e) {
    echo $e::class, ": ", $e->getMessage(), PHP_EOL;
}
Uri\WhatWg\Url::parse("https://user:pass@", null, $e);
var_dump($e);
```

Resulted in this output:
```
Uri\WhatWg\InvalidUrlException: The specified URI is malformed
array(2) {
  [0]=>
  object(Uri\WhatWg\UrlValidationError)#6 (3) {
    ["context"]=>
    string(0) ""
    ["type"]=>
    enum(Uri\WhatWg\UrlValidationErrorType::InvalidCredentials)
    ["failure"]=>
    bool(false)
  }
  [1]=>
  object(Uri\WhatWg\UrlValidationError)#7 (3) {
    ["context"]=>
    string(1) "@"
    ["type"]=>
    enum(Uri\WhatWg\UrlValidationErrorType::InvalidCredentials)
    ["failure"]=>
    bool(false)
  }
}
```

But I expected this output instead:
```
Uri\WhatWg\InvalidUrlException: The specified URI is malformed (HostMissing)
array(2) {
  [0]=>
  object(Uri\WhatWg\UrlValidationError)#6 (3) {
    ["context"]=>
    string(0) ""
    ["type"]=>
    enum(Uri\WhatWg\UrlValidationErrorType::HostMissing)
    ["failure"]=>
    bool(true)
  }
  [1]=>
  object(Uri\WhatWg\UrlValidationError)#7 (3) {
    ["context"]=>
    string(1) "@"
    ["type"]=>
    enum(Uri\WhatWg\UrlValidationErrorType::InvalidCredentials)
    ["failure"]=>
    bool(false)
  }
}
```

The URL specification specifies the following fatal validation error type in step 2.2.1 of the authority state:
> If atSignSeen is true and buffer is the empty string, [host-missing](https://url.spec.whatwg.org/#host-missing) [validation error](https://url.spec.whatwg.org/#validation-error), return failure.

This is tested by the (incorrect) PHP test [whatwg/parsing/host_error_empty2.phpt](https://github.com/php/php-src/blob/4afc970827a038e380551cc97e9a14493cae0854/ext/uri/tests/whatwg/parsing/host_error_empty2.phpt).

### PHP Version

```plain
PHP 8.5.8 (cli) (built: Jul  1 2026 16:35:50) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.5.8, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.8, Copyright (c), by Zend Technologies
```

### Operating System

Arch Linux