Display non-UTF8 commit messages at least partially

[Boddlnagg]

Describe the bug
Currently when a commit message contains invalid UTF8, the whole message is replaced by the string <unknown>.

To Reproduce
Create a Git commit with a message that contains invalid UTF8.

Expected behavior
I think it would be more useful to use replacement characters (i.e. lossy decoding), so at least most of the commit message is displayed correctly if it only contains a single non-UTF8 character somewhere.

[extrawurst]

@Boddlnagg thanks for reporting this, good point! It should be fixed now, but you have no idea how hard it was to force invalid utf8 down rusts safe throat. even the git shell fixed up broken utf8 commit message files. If you could build and test gitui on master to make sure your repro cases are fixed would be awesome!

[Boddlnagg]

Yes, it works now! Thanks for the quick fix 👍

[extrawurst]

Great! @Boddlnagg thanks for checking!

[extrawurst]

released in 0.8 now: https://github.com/extrawurst/gitui/releases/tag/v0.8.0