fix: #62 display a message if user delete the page if only one page;

当只有一页的时候，提示用户至少需要保留一页

front-end/h5/src/store/modules/page.js

@@ -1,3 +1,15 @@
+/*
+ * @Author: ly525
+ * @Date: 2019-12-08 17:05:09
+ * @LastEditors: ly525
+ * @LastEditTime: 2019-12-15 15:41:56
+ * @FilePath: /luban-h5/front-end/h5/src/store/modules/page.js
+ * @Github: https://github.com/ly525/luban-h5
+ * @Description: page module
+ * @Copyright 2018 - 2019 luban-h5. All Rights Reserved
+ */
+import { message } from 'ant-design-vue'
+
 import Page from '../../components/core/models/page'
 
 // actions
@@ -29,7 +41,12 @@ export const mutations = {
         state.work.pages.push(state.editingPage.clone())
         break
       case 'delete':
-        if (state.work.pages.length === 1) return // #!zh: 作品中至少需要保留一个页面，TODO 需要在页面中提示用户此信息
+        if (state.work.pages.length === 1) {
+          // #!zh: 作品中至少需要保留一个页面
+          // #!en: At least one page needs to be kept in the work
+          message.info(`作品中至少需要保留一个页面`)
+          return
+        }
 
         const { work, editingPage } = state
         let index = work.pages.findIndex(page => page.uuid === editingPage.uuid)