fix[sidebar]:fixed when sidebar item only has one children but nested #327

src/views/layout/components/Sidebar/SidebarItem.vue

 <template>
   <div class="menu-wrapper">
-    <template v-for="item in routes">
+    <template v-for="item in routes" v-if="!item.hidden&&item.children">
 
-      <router-link v-if="!item.hidden&&item.children&&item.children.length===1" :to="item.path+'/'+item.children[0].path" :key="item.children[0].name">
+      <router-link v-if="item.children.length===1 && !item.children[0].children" :to="item.path+'/'+item.children[0].path" :key="item.children[0].name">
         <el-menu-item :index="item.path+'/'+item.children[0].path" class='submenu-title-noDropdown'>
           <svg-icon v-if="item.children[0].meta&&item.children[0].meta.icon" :icon-class="item.children[0].meta.icon"></svg-icon>
           <span v-if="item.children[0].meta&&item.children[0].meta.title">{{generateTitle(item.children[0].meta.title)}}</span>
         </el-menu-item>
       </router-link>
 
-      <el-submenu v-if="!item.hidden&&item.children&&item.children.length>1" :index="item.name||item.path" :key="item.name">
+      <el-submenu v-else :index="item.name||item.path" :key="item.name">
         <template slot="title">
           <svg-icon v-if="item.meta&&item.meta.icon" :icon-class="item.meta.icon"></svg-icon>
           <span v-if="item.meta&&item.meta.title">{{generateTitle(item.meta.title)}}</span>
         </template>
 
-        <template v-if="!child.hidden" v-for="child in item.children">
+        <template v-for="child in item.children" v-if="!child.hidden">
           <sidebar-item class="nest-menu" v-if="child.children&&child.children.length>0" :routes="[child]" :key="child.path"></sidebar-item>
 
           <router-link v-else :to="item.path+'/'+child.path" :key="child.name">