Errors thrown here cause 404 error handling to fail. 404s cant url resolve.

After much adventure through error handling in Django-ESI, AA, then Django itself. The root cause of #1399 (closed) was established to be an issue in Navactive.

Aaron and I dubugged this together and came to the conclusion this was likely always an issue, but either v3's error handling (which was all redirects) didnt run into this issue, or some internal improvements to django 404s (and APPEND_SLASH which was originally thought to be the issue) have thrown this.

Our Error handling doesn't have valid urls for navactive to resolve, causing the page renders to loop/throw other errors and not call the APPEND_SLASH handling. Django's exception handling code is slightly different in DEBUG meaning we havent run into this during development.

All we've done here is except out our 404's throwing more 404's and fall down to passing the empty navactive class.