Fix multichar offset issue

[Owen000]

#465

This address the above issue, I'm not 100% confident on why this works but it does. I've done quite a bit of testing and see no downsides to this fix.

[polirritmico]

Hi, the problem with this approach is that sometimes when resizing small windows sizes, the col position minus the offset could be negative instead of 0, throwing an error. Its difficult to reproduce it but it happens (check #461).

I've try it with #470 and work without problems.