[Bug #750] Fix bug

The problem was that a milestone can be a top level task and doesn't
have an associated order element. If the parent of the top level task
is retrieved, the taskgroup associated to the order is returned and
from this taskgroup the order can always be obtained.

FEA: ItEr65S06BugFixing

navalplanner-webapp/src/main/java/org/navalplanner/web/planner/taskedition/TaskPropertiesController.java

@@ -249,7 +249,7 @@ public class TaskPropertiesController extends GenericForwardComposer {
     private Order findOrderIn(IContextWithPlannerTask<TaskElement> context) {
         TaskElement topTask = context.getMapper().findAssociatedDomainObject(
                 findTopMostTask(context));
-        return topTask.getOrderElement().getOrder();
+        return topTask.getParent().getOrderElement().getOrder();
     }
 
     private org.zkoss.ganttz.data.Task findTopMostTask(