fix crash when "Incidence" doesn't exist (crash reproductable when we "undo" a "Complete Purge")
fix crash when "Incidence" doesn't exist
(crash reproductable when we "undo" a "Complete Purge")

svn path=/trunk/kdepim/; revision=303351

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