Inja templates no block default rendering in extends templates

There is a bug in inja where given a template:

`skeleton.txt:`
```
{% block data %}some data{% endblock %}
```
`using_skeleton.txt`:
```
{% extends "skeleton" %}
```
If the subconfig does not define anything, it will be generated as empty instead of using the default value. It is fixed by https://github.com/pantor/inja/pull/332. Could I get a review there?