Fix bug where nil cells would sometimes render without styling

backends/x/draw.go

@@ -49,8 +49,17 @@ func (backend *Backend) drawCells (forceRedraw bool) (areas []image.Rectangle) {
 
 		cell := backend.application.GetForRendering(x, y)
 		content := cell.Rune()
+		style   := cell.Style()
 
-		if forceRedraw && content < 32 { continue }
+		if
+			forceRedraw &&
+			content < 32 &&
+			style & (
+				stone.StyleHighlight |
+				stone.StyleUnderline) == 0 {
+			
+			continue
+		}
 
 		areas = append(areas, backend.boundsOfCell(x, y))
 		backend.drawRune (