Provide more accurate error message

Author: rstoyanchev

spring-websocket/src/main/java/org/springframework/web/socket/messaging/StompSubProtocolHandler.java

@@ -205,7 +205,7 @@ private void publishEvent(ApplicationEvent event) {
 			this.eventPublisher.publishEvent(event);
 		}
 		catch (Throwable ex) {
-			logger.error("Failed to publish event " + event, ex);
+			logger.error("Error while publishing " + event, ex);
 		}
 	}