fix selectExcel bug

src/views/excel/selectExcel.vue

@@ -66,6 +66,7 @@
         this.multipleSelection = val;
       },
       handleDownload() {
+        if (this.multipleSelection.length) {
           require.ensure([], () => {
             const { export_json_to_excel } = require('vendor/Export2Excel');
             const tHeader = ['序号', '文章标题', '作者', '阅读数', '发布时间'];
@@ -75,6 +76,12 @@
             export_json_to_excel(tHeader, data, '列表excel');
             this.$refs.multipleTable.clearSelection();
           })
+        } else {
+          this.$message({
+          message: '请选择一条或多条记录导出',
+          type: 'warning'
+          });
+        }
       },
       formatJson(filterVal, jsonData) {
         return jsonData.map(v => filterVal.map(j => v[j]))