TestNode: do not fail when an invalidated test suite has no distributor set

bt5/erp5_test_result/SkinTemplateItem/portal_skins/erp5_test_result/TaskDistributorAlarm_optimize.xml

@@ -70,6 +70,7 @@ for test_node in list_node:\n
       if ping_date <= old_date:\n
         test_node.invalidate()\n
   elif validation_state == \'invalidated\':\n
+    if test_node.getSpecialise():\n
       test_node.getSpecialiseValue().cleanupInvalidatedTestNode(test_node)\n
 \n
 portal = context.getPortalObject()\n