Add configuration to return False if `of obj` is specifed but `obj` is None.

[lambdalisue]

Currently when obj context is not exists in the template, something like {% if user has 'app_label.change_model' of obj %} return non object permission.

It is a correct behavior but usually non object permission should return True based on basic django concept (https://code.djangoproject.com/wiki/RowLevelPermissions) thus the following code will render links for chaning/deleting the object even if the accessed user does not have such permissions for the object.

{# assume if obj is None or context does not have obj #}
{% if user has 'foo.change_bar' of obj %}
<a href="{% url 'foo_bar_change' pk=obj.pk %}">Change</a>
{% endif %}
{% if user has 'foo.delete_bar' of obj %}
<a href="{% url 'foo_bar_delete' pk=obj.pk %}">Delete</a>
{% endif %}

It is quite annoying thus add PERMISSION_RETURN_FALSE_IF_NONE_IN_TEMPLATE or whatever configuration and check obj value at https://github.com/lambdalisue/django-permission/blob/master/src/permission/templatetags/permissionif.py#L38 and return False if of obj keyword is specified but obj is None.