fix: always render horizontal border edge when enabled (#211)

When a style has a border set and an empty string is rendered, it should
still render the border. When the left border is set, width is
incremented by 1, so in most cases the width will not be 0.

When we render an empty string, with a double border and no left border
we expect the following:
╗
║
╝
But if we don't render a horizontal edge when the string width is less
than 1 we see this:

║

The string width can't be lower than 0, so we can safely remove the
(width < 1) check to create the expected behavior.

Co-authored-by: Daan Schoone <daaschoone@gmail.com>

borders.go

@@ -376,10 +376,6 @@ func (s Style) applyBorder(str string) string {
 
 // Render the horizontal (top or bottom) portion of a border.
 func renderHorizontalEdge(left, middle, right string, width int) string {
-	if width < 1 {
-		return ""
-	}
-
 	if middle == "" {
 		middle = " "
 	}