[#72] Position undo store allow jump back

Author: cpiber

src/scripts/page/player.ts

@@ -289,7 +289,9 @@ const keydownHandler = (e: KeyboardEvent) => {
       sendMessage(Message.QUEUE_PREV, null, false);
       break;
     case 'z':
+      const curPos = player.currentTime;
       if (lastPositon != undefined) player.currentTime = lastPositon;
+      lastPositon = curPos;
       break;
     default:
       return;