Fixed #11381 -- `GeoManager` + `select_related` + nullable `ForeignKey` now...

Fixed #11381 -- `GeoManager` + `select_related` + nullable `ForeignKey` now works correctly.  Thanks, bretthoerner for ticket and dgouldin for initial patch.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@11123 bcc190cf-cafb-0310-a4f2-bffc1f526a37