fix: 修复 app-v3 picker 组件 时间和日期未设置 value 时报错的问题

src/platforms/app-plus/view/components/picker/index.vue

@@ -27,6 +27,7 @@ function padLeft (num) {
   return num > 9 ? num : (`0${num}`)
 }
 function getDate (str, mode_) {
+  str = String(str || '')
   const date = new Date()
   if (mode_ === mode.TIME) {
     str = str.split(':')