Disable button menu hunk there are no changes

[Angelk90]

Summary

If there are no changes in the file, it would be best to disable these two buttons in the menu.

Actual Behavior:

Zed Version and System Specs

Zed: v0.184.0 (Zed Nightly 5ebb18c47e5fc283e2afada6dd434be33f0618e6) 
OS: macOS 15.3.0
Memory: 16 GiB
Architecture: x86_64

[notpeter]

Thanks for reporting. Happy to review PRs.