korganizer: fixed SEGFAULT when deleting recurring TODOs.

This resolves bug 2335 and 2682.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>
(cherry picked from commit 4e2582d3eb)

libkcal/calendar.cpp

@@ -479,8 +479,10 @@ bool Calendar::deleteIncidence( Incidence *incidence )
       IncidenceList il = incidence->childIncidences();
       IncidenceListIterator it;
       it = il.begin();
-      parentIncidence = this->incidence(*it);
-      parentIncidence->deleteChildIncidence(incidence->uid());
+      if (it != il.end()) {
+      	parentIncidence = this->incidence(*it);
+      	parentIncidence->deleteChildIncidence(incidence->uid());
+      }
     }
     else {
       // Delete all children as well