Ignore inline header border when hiding separator

Inline header is drawn inside list border, not adjacent to input
section. Decide based on section actually next to input: header lines
window or list border.

  # Bare header lines next to input; separator needed
  fzf --list-border --header foo --header-lines 2 \
      --header-border inline --header-lines-border none

src/terminal.go

@@ -1734,8 +1734,10 @@ func (t *Terminal) separatedByBorder() bool {
 
 	// The input section has its own window. Determine which section it is
 	// facing, and check if the border of that section draws a line toward it.
-	if hasHeaderWindow && !t.headerFirst {
-		// Header section
+	if hasHeaderWindow && !t.headerFirst && t.headerBorderShape != tui.BorderInline {
+		// Header section; an inline header is not a separate section, it is
+		// drawn inside the list border, so it falls through to the branches
+		// below
 		return t.borderFacingInput(t.headerBorderShape)
 	}
 	// The header lines section is next to the input section, except in