br/stream: `log status` panics when encountering incompatible versions

[YuJuncen]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Start a nightly cluster.
2. Run br log status.

2. What did you expect to see? (Required)

BR should fail with message "incompatible".

3. What did you see instead (Required)

BR paniced.

4. What is your TiDB version? (Required)

Master.

NOTE: The error was omitted at https://github.com/pingcap/tidb/pull/56075/files#diff-82ee5900311f16cef9a19f0efdc01606af750a36a92365bc7ac68bfb010eef44R186