[Bug] ClusterMessageService.batchAckMessage throws on empty handle list

### Before Creating the Bug Report

- [x] I have searched the existing issues and pull requests.

### Runtime platform environment

N/A

### RocketMQ version

develop branch

### JDK Version

N/A

### Describe the Bug

`ClusterMessageService.batchAckMessage()` builds `extraInfoList` from `handleList` and then immediately reads `handleList.get(0)` to resolve the broker address.

If an empty handle list reaches this service method, it throws `IndexOutOfBoundsException` before returning a failed future with a meaningful Proxy error.

### Steps to Reproduce

1. Call `ClusterMessageService.batchAckMessage()` with an empty `handleList`.
2. Observe that `handleList.get(0)` is evaluated without a non-empty guard.

### What Did You Expect to See?

The method should reject an empty batch ack request with a stable failed future and a meaningful Proxy error. It should not call the broker client because there is no receipt handle from which a broker can be resolved.

### What Did You See Instead?

The method can throw `IndexOutOfBoundsException`.

### Additional Context

This is a small Proxy runtime robustness fix for the batch ack path.

Start at ClusterMessageService.batchAckMessage() and trace how handleList is converted into extraInfoList and used to resolve the broker address. Exercise the method with an empty handleList, then verify it returns a stable failed future with a meaningful Proxy error without calling the broker client.

Written by the indexing model from the issue text.