Prevent KeyError when page_template not supplied
Prevent KeyError when page_template not supplied

When `page_template` is not supplied as a kwarg via `.as_View()` a
KeyError is raised because `.pop()` is used on a dictionary with no
default value specified.

catalpainternational/django-endless-pagination,igorkramaric/django-endless-pagination,kjefes/django-endless-pagination,kjefes/django-endless-pagination,catalpainternational/django-endless-pagination,frankban/django-endless-pagination,kjefes/django-endless-pagination,frankban/django-endless-pagination,igorkramaric/django-endless-pagination,kjefes/django-endless-pagination,suchanlee/django-endless-pagination,suchanlee/django-endless-pagination,igorkramaric/django-endless-pagination,frankban/django-endless-pagination,suchanlee/django-endless-pagination,catalpainternational/django-endless-pagination,igorkramaric/django-endless-pagination,catalpainternational/django-endless-pagination