feat:下载文档间距问题

jydocs-pc/src/views/Content.vue

@@ -479,9 +479,9 @@ export default {
       this.$nextTick(() => {
         // 获取到达页面顶端的值
         const heights = document.getElementById('fixedTop')
-        this.offsetTop = heights.getBoundingClientRect().top
+        this.offsetTop = heights ? heights.getBoundingClientRect().top : 0
         const headerNav = document.getElementById('public-nav')
-        if (headerNav) {
+        if (headerNav && heights) {
           const headerTop = headerNav.offsetHeight
           heights.style.top = headerTop + 'px'
         }