Prevent infinite loops for empty props element

[rullzer]

If you do a propfind with:

<?xml version="1.0"?>
<a:propfind xmlns:a="DAV:">
  <a:prop></a:prop>
</a:propfind>

And have this parsed:

use Sabre\DAV\Xml\Service;

$content = '<?xml version="1.0"?><a:propfind xmlns:a="DAV:"><a:prop></a:prop></a:propfind>';

$xml = new Service();
$xml->expect('{DAV:}propfind', $content);

Then this results in an infinite loop. This patch breaks out of the loop once the reader fails to read.

[LorbusChris]

@rullzer any progress on this?

[rullzer]

It is still dangling somewhere on my todo... But that todo is long