[youzan/vant-weapp]DateTimePicker在切换type后发生异常

描述一下问题

我先是设置了选择器为date，弹出选择完关闭后又设置type为“year-month”,然后在滑动滚轮选择的时候发生如下异常。愿尽快修复，谢谢~

环境

• 设备: IDE模拟工具
• 基础库版本: 2.41
• Vant Weapp 版本:vant-weapp-0.4.8

VM41449:1 thirdScriptError Cannot read property '5' of undefined; [Component] Event Handler Error @ src/components/vant/datetime-picker/index#onChange TypeError: Cannot read property '5' of undefined at http://127.0.0.1:45289/appservice/src/components/vant/datetime-picker/index.js:265:36 at Array.map () at V.onChange (http://127.0.0.1:45289/appservice/src/components/vant/datetime-picker/index.js:264:32) at Object.r.safeCallback (http://127.0.0.1:45289/appservice/__dev__/WAService.js:1:463149) at http://127.0.0.1:45289/appservice/__dev__/WAService.js:1:542632 at d (http://127.0.0.1:45289/appservice/__dev__/WAService.js:1:544835) at http://127.0.0.1:45289/appservice/__dev__/WAService.js:1:544147 at n (http://127.0.0.1:45289/appservice/__dev__/WAService.js:1:171394) at e (http://127.0.0.1:45289/appservice/appservice?t=1544098389944:7110:20307) at r.registerCallback.t (