scxtop: rendering breaks on large displays

[JakeHillion]

When rendered at low zoom levels on large displays scxtop's rendering starts getting funky.

Failure case (4K monitor at my normal zoom level):

The boxing of view elements seems to have wrapped around somehow. The dynamic parts still render properly, but the static parts are messed up.

Super failure case (4K monitor really zoomed out):

This one gets really weird. More of the same I think. The dynamic bit still renders properly.

Should look like (Cmd + a couple of times from the normal zoom level):

cc @hodgesds

[etsal]

Just to add to this, rendering also breaks for small displays: When the tmux window is too small the UI refuses to load at all.