Prevent accidental handling of errors during preview rendering.
Prevent accidental handling of errors during preview rendering.

Summary:
This prevents exceptions (specifically KeyError) being erroneously
caught and rewrapped as Http404 exceptions when they occur while
rendering a message.

Reviewers: jeff, branden, matt

Reviewed By: matt

Differential Revision: http://phabricator.local.disqus.net/D7729

danxshap/django-mailviews,joshowen/django-mailviews,xavierdutreilh/django-mailviews,danxshap/django-mailviews,paxnovem/django-mailviews,disqus/django-mailviews,joshowen/django-mailviews,paxnovem/django-mailviews,xavierdutreilh/django-mailviews,disqus/django-mailviews