No rendering when code has no closing tag

Hello there,

In case the plugin is still maintained, reporting a bug (that may be caused by a regression in WP's shortcode API, because that bug wasn't there 15 years ago :)

This renders fine : 

```
[php]
<?php
echo "ok";
?>
[/php]
```

This doesn't render, the shortcode is ignored :

```
[php]
<?php
echo "ok";
[/php]
```