Fix a race condition between ShardConsumer shutdown and initialization

amazon-kinesis-client/src/main/java/software/amazon/kinesis/lifecycle/ShardConsumer.java

@@ -179,8 +179,18 @@ public void executeLifecycle() {
                         // Task rejection during the subscribe() call will not be propagated back as it not executed
                         // in the context of the Scheduler thread. Hence we should not assume the subscription will
                         // always be successful.
+                        // But if subscription was not successful, then it will recover
+                        // during healthCheck which will restart subscription.
+                        // From Shardconsumer point of view, initialization after the below subscribe call
+                        // is complete
                         subscribe();
                         needsInitialization = false;
+                        // Initialization is complete, return now, because we dont need to do
+                        // initializeComplete anymore. ShardConsumer is in ProcessingState now and any further activity
+                        // will be driven by publisher pushing data to subscriber which invokes handleInput
+                        // and that triggers ProcessTask. Scheduler is only meant to do health-checks
+                        // to ensure the consumer is not stuck for any reason and to do shutdown handling.
+                        return;
                     }
                 }
                 stateChangeFuture = initializeComplete();