Cursor position is not updated when navigating with commands other than `up` and `down`

[ducaale]

It would be nice if fx's cursor behaved similarly to text editors which always have their cursor in the viewport when jumping around.

Steps to reproduce:

1. Run curl -s https://jsonplaceholder.typicode.com/posts | fx
2. Use one of many supported keybindings to jump around e.g. G
3. Use either j or k to move one line up or down. This will cause the viewport to jump to the last position of the cursor.