fixed bug which calls persistency service before init

refs 1376

org.fortiss.tooling.kernel/trunk/src/org/fortiss/tooling/kernel/internal/storage/eclipse/ModelContext.java

@@ -202,7 +202,9 @@ class ModelContext implements ITopLevelElement, CommandStackListener {
 		((BasicCommandStack)editingDomain.getCommandStack()).saveIsDone();
 		performNotifyListeners(editingDomain.getCommandStack());
 
-		IPersistencyService.INSTANCE.notifyTopLevelElementChanged(ModelContext.this);
+		if(IPersistencyService.INSTANCE != null) {
+			IPersistencyService.INSTANCE.notifyTopLevelElementChanged(ModelContext.this);
+		}
 
 		monitor.done();
 	}