[0.5.X] Fixed #9462 -- Set the instance in an inline formset correctly so that...

[0.5.X] Fixed #9462 -- Set the instance in an inline formset correctly so that None does not get passed through to the queryset. Thanks tobias and copelco for the ticket.

Backport of r9293 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9294 bcc190cf-cafb-0310-a4f2-bffc1f526a37