add remove item and remove all in discount

app/views/origami/discounts/index.html.erb

@@ -369,10 +369,19 @@ $(document).ready(function(){
 
 		// Selected Items		
 		var sale_items = get_selected_sale_items();	
+		if(sale_items.length == 0){
+			alert("You have no selected item!");
+			return;
+		}
+
 		for(var i=0;i < sale_items.length;i++){
 			if(sale_items[i].price < 0){
 				discount_items.push(sale_items[i]);
 			}
+			else {
+				alert("You have selected no discount item!");
+				return;
+			}
 		}
 
 		var params = { 'sale_id': sale_id, 'discount_items': JSON.stringify(discount_items) };