Fix regression where tcell renderer not clearing the preview window

src/tui/light.go

@@ -1109,3 +1109,7 @@ func (w *LightWindow) Erase() {
 	w.FinishFill()
 	w.Move(0, 0)
 }
+
+func (w *LightWindow) EraseMaybe() bool {
+	return false
+}

src/tui/tcell.go

@@ -555,6 +555,11 @@ func (w *TcellWindow) Erase() {
 	fill(w.left-1, w.top, w.width+1, w.height-1, w.normal, ' ')
 }
 
+func (w *TcellWindow) EraseMaybe() bool {
+	w.Erase()
+	return true
+}
+
 func (w *TcellWindow) Enclose(y int, x int) bool {
 	return x >= w.left && x < (w.left+w.width) &&
 		y >= w.top && y < (w.top+w.height)

src/tui/tui.go

@@ -526,6 +526,7 @@ type Window interface {
 	Fill(text string) FillReturn
 	CFill(fg Color, bg Color, attr Attr, text string) FillReturn
 	Erase()
+	EraseMaybe() bool
 }
 
 type FullscreenRenderer struct {