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

@@ -479,9 +479,11 @@ bool Calendar::deleteIncidence( Incidence *incidence )
       IncidenceList il = incidence->childIncidences();
       IncidenceListIterator it;
       it = il.begin();
+      if (it != il.end()) {
       	parentIncidence = this->incidence(*it);
       	parentIncidence->deleteChildIncidence(incidence->uid());
       }
+    }
     else {
       // Delete all children as well
       IncidenceList il = incidence->childIncidences();