Can't run `merge --no-ff` if there aren't enough commit

[Michelle Tilley]

Logic in HistoryView runs off the left edge of the commit graph causing errors; as long as the branch being merged is at least 3 commits in, --no-ff works fine.

[Ian Lee]

Just found this myself. Seems to be the code bit here: https://github.com/git-school/visualizing-git/blob/gh-pages/js/historyview.js#L1419

[Connor]

I'm seeing this issue as well with same precondition.