Restore scroll after rendering full-height Sixel image (#2544)

When a Sixel image touches the bottom of the screen, the whole screen
scrolls up one line to make room for the cursor. Add an ANSI escape
code to compensate for the movement. Unfortunately, the movement of the
screen is sometimes noticeable.

  fzf --preview='fzf-preview.sh {}' --preview-window border-left

src/terminal.go

@@ -2061,7 +2061,10 @@ Loop:
 
 				if requiredLines > 0 {
 					if y+requiredLines == height {
-						t.pwindow.Move(y+requiredLines, 0)
+						if t.tui.MaxY() == t.pwindow.Top()+height {
+							t.tui.PassThrough("\x1b[1T")
+						}
+						t.pwindow.Move(height-1, maxWidth-1)
 						t.previewed.filled = true
 						break Loop
 					} else {