Description
-----------

| Q                | A
| -----------------| ---
| Fixed issues     | -
| Docs PR or issue | Related to contao/docs#322

While working on an example for contao/docs#322 I noticed a possible problem within the current `RobotsTxtListener` of Contao. No matter what I tried, the resulting `robots.txt` was always

```
user-agent:*
disallow:/foo/
disallow:/contao/

user-agent:*
disallow:/contao/
```

instead of

```
user-agent:*
disallow:/foo/
disallow:/contao/
```

when using the following `App\EventListener\RobotsTxtListener`:

```php
// src/EventListener/RobotsTxtListener.php
namespace App\EventListener;

use Contao\CoreBundle\Event\ContaoCoreEvents;
use Contao\CoreBundle\Event\RobotsTxtEvent;
use Terminal42\ServiceAnnotationBundle\Annotation\ServiceTag;
use Terminal42\ServiceAnnotationBundle\ServiceAnnotationInterface;
use webignition\RobotsTxt\Directive\Directive;
use webignition\RobotsTxt\Record\Record;

/**
 * @ServiceTag("kernel.event_listener", event=ContaoCoreEvents::ROBOTS_TXT)
 */
class RobotsTxtListener implements ServiceAnnotationInterface
{
    public function __invoke(RobotsTxtEvent $event): void
    {
        $file = $event->getFile();

        // If no directive for user-agent: * exists, we add the record
        if (0 === count($file->getRecords())) {
            $record = new Record();
            $this->addDirectivesToRecord($record);
            $file->addRecord($record);
        }

        foreach ($file->getRecords() as $record) {
            $this->addDirectivesToRecord($record);
        }
    }

    private function addDirectivesToRecord(Record $record): void
    {
        $directiveList = $record->getDirectiveList();
        $directiveList->add(new Directive('Disallow', '/foo/'));
    }
}
```

The `App\EventListener\RobotsTxtListener` is actually executed before the `Contao\CoreBundle\EventListener\RobotsTxtListener` (when using no priority setting). So, even though `App\EventListener\RobotsTxtListener` already added a record, the following check still holds true:

https://github.com/contao/contao/blob/7de5fddec93c9a575166296da06e40a5f3e1c9b9/core-bundle/src/EventListener/RobotsTxtListener.php#L42-L52

This PR simply counts the returned records directly - but may be I am overlooking something here.

Commits
-------

c0b4b126 fix robots.txt listener
0649ea9c add user-agent directive
9c18d11a remove superfluous function
cc9c51a8 undo comment change
5d7302b9 adjust test