[Android]fix jira problems: NMS-5470

Author: xgfd3

Android/APIExample/app/src/main/java/io/agora/api/example/examples/advanced/RTMPStreaming.java

@@ -161,6 +161,9 @@ public void onDestroy()
             engine.leaveChannel();
             engine.stopPreview();
         }
+        if(retryTask != null){
+            retryTask.cancel(true);
+        }
         handler.post(RtcEngine::destroy);
         engine = null;
     }