wrong content-type & content-length on dynamic large object

If `$dlo` is a [large-object](https://docs.openstack.org/swift/latest/overview_large_objects.html#direct-api):
```php
$container->getObject($dlo)
// [contentType] =>  null
// [contentLength] => null
```
`swift stat` on the same file:
```
Content Type: application/octet-stream
Content Length: 8389723
```

Quite related to https://github.com/php-opencloud/openstack/issues/285