Fixed #7369: fixed a corner-case involving select_related() following non-null...

Fixed #7369: fixed a corner-case involving select_related() following non-null FKs after null ones. Thanks, George Vilches


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7597 bcc190cf-cafb-0310-a4f2-bffc1f526a37