fix: 背景图片空url 问题

frontend/src/views/panel/list/EditPanel/index.vue

@@ -58,9 +58,13 @@ export default {
   },
   computed: {
     classBackground() {
+      if (this.importTemplateInfo.snapshot) {
         return {
           background: `url(${this.importTemplateInfo.snapshot}) no-repeat`
         }
+      } else {
+        return {}
+      }
     }
   },
   watch: {