adds fix for SingleObjectTemplateResponseMixin raising a TemplateDoesNotExist when it should have raised an ImproperlyConfigured. fixes 16502. by @ianawilson, @jambonrose
fixed test name from an old, overly specific iteration of the test
Merge pull request #1580 from ianawilson/ticket_16502

Fixed #16502 -- Fixed a TemplateDoesNotExist error that should be an ImproperlyConfigured.

Assistance on the patch from #jambronrose.