notify when client connection lost；

implement onConnectionLost() method in AbstractInterceptHandler.java;

broker/src/main/java/io/moquette/interception/AbstractInterceptHandler.java

@@ -30,6 +30,9 @@ public abstract class AbstractInterceptHandler implements InterceptHandler {
     @Override
     public void onDisconnect(InterceptDisconnectMessage msg) {}
 
+    @Override
+    public void onConnectionLost(InterceptConnectionLostMessage msg) {}
+
     @Override
     public void onPublish(InterceptPublishMessage msg) {}
 

broker/src/test/java/io/moquette/spi/impl/BrokerInterceptorTest.java

@@ -51,6 +51,11 @@ public class BrokerInterceptorTest {
             n.set(50);
         }
 
+        @Override
+        public void onConnectionLost(InterceptConnectionLostMessage msg) {
+            n.set(30);
+        }
+
         @Override
         public void onPublish(InterceptPublishMessage msg) {
             n.set(60);