Adding safety check around stopwatches

amazon-kinesis-client/src/main/java/software/amazon/kinesis/leases/LeaseCleanupManager.java

@@ -82,12 +82,15 @@ public class LeaseCleanupManager {
      */
     public void start() {
         log.debug("Starting lease cleanup thread.");
-        isRunning = true;
-        completedLeaseStopwatch.start();
-        garbageLeaseStopwatch.start();
+
+        if (!isRunning) {
+            completedLeaseStopwatch.start();
+            garbageLeaseStopwatch.start();
+        }
 
         deletionThreadPool.scheduleAtFixedRate(new LeaseCleanupThread(), INITIAL_DELAY, leaseCleanupIntervalMillis,
                 TimeUnit.MILLISECONDS);
+        isRunning = true;
     }
 
     /**