fix for replies breaking on forum posts not associated with projects. PMT #96468

Old forum posts, and posts made through the Perl version, when not
associated with a project, get a '0' as the project id for that column
instead of a NULL. Django does the right thing on creating them
and consistently sets it to NULL, but we still need to deal with the
old data for a while longer.
release under GPL >= 2
make jscs happy
Merge pull request #138 from thraxil/reply-to-forum-post-not-in-project

fix for replies breaking on forum posts not associated with projects. PM...