Editor crash when undoing at list end

[hypest]

(First reported in #208 (comment) by @mkevins)

Undoing the newly added list item produces a red-screen.

Steps to reproduce:

1. Add a new list block
2. Type in few chars in the first line item and hit Enter to start a new item
3. Type in some more chars
4. Hit the "Undo" toolbar button
5. 💥

[mchowning]

I believe this issue has recently been fixed. I was seeing this issue on Android before I merged in the latest today from gutenberg, but post-merge I am not able to recreate it anymore.

[hypest]

Indeed, I cannot reproduce it, at least on a29bec3. Closing this.