fix 单选按钮只读模式下，获取默认值的逻辑优化

 <!--
  * @Date: 2022-08-30 11:34:19
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2024-07-26 22:13:18
+ * @LastEditTime: 2024-07-30 10:07:43
  * @FilePath: /data-table/src/components/RadioField/index.vue
  * @Description: 单项选择控件
 -->
@@ -146,6 +146,8 @@ onMounted(() => {
           element.affix = part2
         }
       });
+  } else {
+    default_value.value = props.item.component_props.default;
   }
   // 发送自定义数据结构
   props.item.value = { key: props.item.key, value: radio_value.value, affix: affix_value.value, type: "radio" };