Fix crash on purge completed todos.
Fix crash on purge completed todos.

svn path=/trunk/kdepim/; revision=337889

lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi