perf[Sidebar]: adapt when no icon

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

@@ -4,7 +4,7 @@
     <template v-if="hasOneShowingChild(item.children) && !onlyOneChild.children&&!item.alwaysShow">
       <a :href="onlyOneChild.path" target="_blank" @click="clickLink(onlyOneChild.path,$event)">
         <el-menu-item :index="resolvePath(onlyOneChild.path)" :class="{'submenu-title-noDropdown':!isNest}">
-          <item v-if="onlyOneChild.meta" :icon="onlyOneChild.meta.icon" :title="onlyOneChild.meta.title" />
+          <item v-if="onlyOneChild.meta" :icon="onlyOneChild.meta.icon||item.meta.icon" :title="onlyOneChild.meta.title" />
         </el-menu-item>
       </a>
     </template>