fix: 背景图片空url 问题

frontend/src/views/panel/template/component/TemplateItem.vue

@@ -22,10 +22,14 @@ export default {
   },
   computed: {
     classBackground() {
+      if (this.template.snapshot) {
         return {
           background: `url(${this.template.snapshot}) no-repeat`,
           'background-size': `100% 100%`
         }
+      } else {
+        return {}
+      }
     }
   },
   methods: {