Problem:
Coordinates-to-position conversion for the finish column in
`vim.hl.range()` checks the start column. This results in an incorrect
finish column when only one of the column coordinates is `vim.v.maxcol`.
Solution:
Check the finish column when converting the finish position. Update the
existing screen test so that a `vim.v.maxcol` finish highlights the
end-of-line marker, matching the existing `-1` behavior.
1c31526a90
