Release cached item in ChannelSendOperator when server error

Related to gh-22720

Author: violetagg

spring-web/src/main/java/org/springframework/http/server/reactive/ChannelSendOperator.java

@@ -394,7 +394,12 @@ public void onNext(Void aVoid) {
 
 		@Override
 		public void onError(Throwable ex) {
-			this.completionSubscriber.onError(ex);
+			try {
+				this.completionSubscriber.onError(ex);
+			}
+			finally {
+				this.writeBarrier.releaseCachedItem();
+			}
 		}
 
 		@Override