7020: Date filtering fails to work on Family Events in 3.4.6 or 4.0.2; typo, missing 'not'

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@22918 4ae1f11a-8b86-4847-b8af-ab372f36d1fd