Always set heart-beat header in STOMP CONNECTED frames

Since SPR-10954, the SimpleBrokerMessageHandler supports `heart-beats`.

Even if the STOMP spec states that the `heart-beat` header is OPTIONAL,
and if absent considered as `heart-beat: 0,0`,
some clients rely on this to be set in CONNECTED frames.

This commit adds this header information even if no task
scheduler/heart-beat have been configured.

See: https://stomp.github.io/stomp-specification-1.2.html#Heart-beating

Issue: SPR-10954

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

@@ -449,6 +449,8 @@ public class StompSubProtocolHandler implements SubProtocolHandler, ApplicationE
 		long[] heartbeat = (long[]) connectAckHeaders.getHeader(SimpMessageHeaderAccessor.HEART_BEAT_HEADER);
 		if (heartbeat != null) {
 			connectedHeaders.setHeartbeat(heartbeat[0], heartbeat[1]);
+		} else {
+			connectedHeaders.setHeartbeat(0, 0);
 		}
 		return connectedHeaders;
 	}