Don't show box chars on waste pile's cards.

src/keyboard.c

@@ -52,6 +52,7 @@ static void handle_stock_event() {
   if (!empty(deck->stock)) {
     move_card(&(deck->stock), &(deck->waste_pile));
     expose_card(deck->waste_pile->card);
+    erase_stack(deck->waste_pile);
     draw_stack(deck->stock);
     draw_stack(deck->waste_pile);
   }