[Bug] ~ followed by an undo enters visual mode #196

Steps to reproduce

1. Go to https://raw.githack.com/replit/codemirror-vim/master/dev/web-demo.html
2. In the normal mode, press ~ to invert the case of any character.
3. Press mod+z to trigger CodeMirror's undo command. (do not use Vim's undo command u)

Expected result

The vim emulator stays in the normal mode, and no text is selected.

Actual result

It goes into the visual mode - in other words, the character under the cursor is selected. If you move the cursor using the arrow or hjkl keys, the selection will expand accordingly.