Undo/redo doesn't seem to work when typing some text

[koke]

To reproduce:

1. Create a new post
2. Start a paragraph
3. Type hello
4. Tap undo: nothing happens (should go back to an empty paragraph)
5. Tap undo: paragraph removed
6. Tap redo: empty paragraph restored
7. Tap redo: "hello" restored (but cursor at the beginning of the paragraph)

I saw this both on iOS and Android

[daniloercoli]

I think i've a quick fix for this.