Fixed|libappfw|ChildWidgetOrganizer: Potential memory access issue

Issue found by Guard Malloc. Since we have an iterator already, it
is better to use it to remove the map entry rather than looking it
up again using the key.

doomsday/libappfw/src/childwidgetorganizer.cpp

@@ -179,12 +179,12 @@ DENG2_OBSERVES(ui::Item, Change     )
 
     void dataItemRemoved(ui::Data::Pos, ui::Item &item)
     {
-        Mapping::const_iterator found = mapping.constFind(&item);
+        Mapping::iterator found = mapping.find(&item);
         if(found != mapping.constEnd())
         {
             found.key()->audienceForChange() -= this;
             deleteWidget(found.value());
-            mapping.remove(found.key());
+            mapping.erase(found);
         }
     }