set the initial value of wrs to scn min

src/sql/engine/subquery/ob_subplan_filter_op.cpp

@@ -602,6 +602,7 @@ int ObSubPlanFilterOp::handle_next_row()
         }
       }
       save_last_row_ = false;
+      set_param_null();
       while (OB_SUCC(ret) && batch_count--) {
         clear_evaluated_flag();
         set_param_null();