Use git log name-status in get last commit (#16059)

* Improve get last commit using git log --name-status

git log --name-status -c provides information about the diff between a
commit and its parents. Using this and adjusting the algorithm to use
the first change to a path allows for a much faster generation of commit
info.

There is a subtle change in the results generated but this will cause
the results to more closely match those from elsewhere.

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Lauris BH <lauris@nix.lv>

modules/git/repo_language_stats_nogogit.go

@@ -49,6 +49,9 @@ func (repo *Repository) GetLanguageStats(commitID string) (map[string]int64, err
 		log("Unable to get commit for: %s. Err: %v", commitID, err)
 		return nil, err
 	}
+	if _, err = batchReader.Discard(1); err != nil {
+		return nil, err
+	}
 
 	tree := commit.Tree