Fix crash on NULL pointer dereference

This resolves Bug 2773

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>

korganizer/koeditorfreebusy.cpp

@@ -850,10 +850,13 @@ void KOEditorFreeBusy::removeAttendee()
 void KOEditorFreeBusy::clearSelection() const
 {
   KDGanttViewItem *item = mGanttView->selectedItem();
-  if ( item )
+  if (item) {
     mGanttView->setSelected( item, false );
+  }
   mGanttView->repaint();
-  item->repaint();
+  if (item) {
+    item->repaint();
+  }
 }
 
 void KOEditorFreeBusy::setSelected( int index )