6448: Text Reports>Descendant Report gives an AttributeError: 'Sort' object has no attribute by_birthdate


git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21357 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
Fixed a typo.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21359 4ae1f11a-8b86-4847-b8af-ab372f36d1fd