git_ui: Fix showing commit history in detached HEAD state

[mertkanakkoc]

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #57783

When a repository is in detached HEAD state (e.g. after git checkout <sha>), the branch field is None and the history tab was silently returning early, showing nothing.

This change falls back to HEAD as the log source when no branch is active, so commit history is displayed from the current HEAD position.

Release Notes:

• Fixed commit history not displaying when repository is in detached HEAD state.

[mertkanakkoc]

before open this pr, i did not see the #57959 . because i only looked the bug issue #57783 whether there is an open pr about this issue or not. It seems that #57959 solves the same fix and more

[smitbarmase]

Thanks, as you pointed out, I'm closing this in favor of #57959.

[mertkanakkoc]

you are welcome :)