Fix off-by-one error for reversed UI-selection

This is a further improvement on #253 where the selection would be non-empty due to an seemingly unnecessary `+ 1`. I want to remove this addition to make sure that a reversed selection isn't suddenly one character longer than intended, deleting more than wanted for the feature requested in #249.

This addition *might* have been necessary at one point, but this seems no longer the case. The visual modes have been completely overhauled since that tiny piece of code was written, and so it's likely that it was simply forgotten about.

I've been testing this one for a while but I couldn't find any problems so far...