feature: Remember commit message when undoing commit

[Kamilcuk]

In git gui I can click "Amend last commit", then the last commit message will show up in the right down corner.

When I click "Undo Commit [U]" in gitui, then try to "Commit [c]", the commit message is empty, and I have to retype it.

Describe the solution you'd like
It would be great if the commit message would be remembered when undoing a commit.

"Undo Commit [U]" in gitui is great, but it does not remember the commit message.

I am so much in love in "Amend Last Commit" in git gui. It is a very easy and flexible way for rebasing commits and splitting them into smaller parts. I would be happy to have this functionality in gitui.

Describe alternatives you've considered
git gui

Additional context

Thanks for making gitui, it is just great.

(Additionally, subjectively, it would be great to show a one-line small window on right bottom below "Diff:" window in git ui to show the temporary commit message, just like git gui does. But I do not need it, this would only be "nice to have".)

[extrawurst]

You can use the commit msg history for that: default key bindings: ctrl-n

[Kamilcuk]

Like a charm! Thank you!