在controller处限制step>0 (#35)

Author: xzchaoo

client/lookout-reg-server/src/main/java/com/alipay/lookout/remote/report/poller/PollerController.java

@@ -240,6 +240,7 @@ public void destroy() {
      * @param newSlotCount
      */
     public synchronized void update(long newStep, int newSlotCount) {
+        Preconditions.checkArgument(newStep >= 0, "step must greater than 0");
         setSlotCount(newSlotCount);
         setStep(newStep);
         registry.setStep(newStep);