fix calendar crash when deleting events in agenda view

calendar is stopped and JAVACRASH occurs after deleting some events in Calendar's Agenda view

Change-Id: I9da477a6ba6ac68327d5f64f44c76618d612a248
Author: Huaqiang Chen <huaqiangx.chen@intel.com>
Signed-off-by: b566 <b566@borqs.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 48926