修复微信openId为null的bug

src/pages/buy/index.vue

@@ -96,6 +96,9 @@ export default {
   beforeMount() {
     this.fetchGoodsDetails()
     this.fetchShopDetails()
+    let openId = window.localStorage.getItem('openId')
+    if (openId === 'undefined' || openId === 'null') openId = ''
+    this.openId = openId // 'oF3a-t9pFpmL2gWuTmtWs5HlDGkU'
     if (this.isWxBrowser && !this.openId) {
       const { code } = this.$route.query
       if (code) this.fetchOpenId(code)