here is a vim option ``selection``.
if the value is `exclusive`, the mark `'>` is one more then real visual selection.
so var `ebyte` or `ec` must subtract 1.
and that is not a windows bug.
because gvim on windows sourced `$VIMRUNTIME\mswin.vim` by default.
the line 17 of `mswin.vim` execute `:behave mswin` will change option `selection` to `exclusive`.
more deailt in issue #863