Merged [7077] from rjsparks@nostrum.com: Returns "there are no ballots to view yet" rather than 404ing when the ballot link is followed for a document that exists.

It is typical for last call to be issued (which includes a link to the ballot page) well in advance of creating any ballot for a document.
Fixes bug 1233
 - Legacy-Id: 7223
Note: SVN reference [7077] has been migrated to Git commit e93b5ec

Author: levkowetz

ietf/doc/views_doc.py

@@ -648,7 +648,7 @@ def document_ballot_content(request, doc, ballot_id, editable=True):
         ballot = all_ballots[-1]
 
     if not ballot:
-        raise Http404
+        return "<p>No ballots are available for this document at this time.</p>"
 
     deferred = doc.active_defer_event()