Fixes "include" tag compilation when parentFile is null

I ran into "Uncaught TypeError: Cannot call method 'replace' of null " during browser client-side rendering.

**Javascript**

    var html = swig.render(tmpl, {'locals': {
        'project': self.model.attributes
    }});

**Template**

    <div class="inner{% if project.is_loading %} loading{% endif %}">
        <div class="thumbnail">
            <a href="{{ project.absolute_url }}"><img alt="{{ project.name }}" src="{{ project.image_card_url }}"></a>
        </div>
        <h3 class="title"><a href="{{ project.absolute_url }}">{{ project.name }}</a></h3>
        <a class="desc">{{ project.description }}</a>
        <div class="actions">
            {% include "project/includes/project_button_activate.html" %}
        </div>
    </div>