Fix ReactiveStreamsConsumer for error handling

To support `onErrorContinue()` logic for the plain `Subscriber`
we need to wrap its `onNext()` into a `try..catch` and respective
`errorHandler` in the `ReactiveStreamsConsumer`

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/endpoint/ReactiveStreamsConsumer.java

@@ -166,21 +166,25 @@ protected void doStart() {
 			this.subscription =
 					Flux.from(this.publisher)
 							.flatMap(this.reactiveMessageHandler::handleMessage)
-							.onErrorContinue(this::onError)
+							.onErrorContinue((ex, data) -> this.errorHandler.handleError(ex))
 							.subscribe();
 		}
 		else if (this.subscriber != null) {
-			Flux.from(this.publisher)
-					.doOnSubscribe((subs) -> this.subscription = subs::cancel)
-					.onErrorContinue(this::onError)
-					.subscribe(this.subscriber);
+			this.subscription =
+					Flux.from(this.publisher)
+							.doOnComplete(this.subscriber::onComplete)
+							.doOnSubscribe(this.subscriber::onSubscribe)
+							.subscribe((data) -> {
+								try {
+									this.subscriber.onNext(data);
+								}
+								catch (Exception ex) {
+									this.errorHandler.handleError(ex);
+								}
+							});
 		}
 	}
 
-	private void onError(Throwable ex, Object data) {
-		this.errorHandler.handleError(ex);
-	}
-
 	@Override
 	protected void doStop() {
 		if (this.subscription != null) {