fix: console error when toggle page

Issue #4
Close #4

src/components/layout/PageView.vue

@@ -21,7 +21,7 @@ export default {
       extraImage: ''
     }
   },
-  mounted () {
+  beforeMount () {
     this.getPageHeaderInfo()
   },
   updated () {
@@ -31,12 +31,14 @@ export default {
     getPageHeaderInfo () {
       this.title = this.$route.name
       const page = this.$refs.page
+      if (page) {
         this.desc = page.desc
         this.linkList = page.linkList
         this.extraImage = page.extraImage
       }
     }
   }
+}
 </script>
 
 <style lang="less" scoped>