Fix NPE when importing config without metadata file

[Senrian]

Bug Description

Issue: #14785

When importing a ZIP configuration file without the required metadata file (.meta.yml or .metadata.yml), the server throws a NullPointerException:

Cannot invoke "com.alibaba.nacos.config.server.utils.ZipUtils$ZipItem.getItemData()" because "metaDataItem" is null

Root Cause

In ConfigControllerV3.parseImportDataV2(), the code directly calls metaDataItem.getItemData() without checking if metaDataItem is null.

Fix

Add a null check before accessing metaDataItem:

ZipUtils.ZipItem metaDataItem = unziped.getMetaDataItem();
Map<String, Object> failedData = new HashMap<>(4);

if (metaDataItem == null) {
    failedData.put("succCount", 0);
    return Result.failure(ErrorCode.METADATA_ILLEGAL, failedData);
}

String metaData = metaDataItem.getItemData();

[github-actions]

Thanks for your this PR. 🙏
Please check again for your PR changes whether contains any usage/api/configuration change such as Add new API , Add new configuration, Change default value of configuration.
If so, please add or update documents(markdown type) in docs/next/ for repository nacos-group/nacos-group.github.io

---

感谢您提交的PR。 🙏
请再次查看您的PR内容，确认是否包含任何使用方式/API/配置参数的变更，如：新增API、新增配置参数、修改默认配置等操作。
如果是，请确保在提交之前，在仓库nacos-group/nacos-group.github.io中的docs/next/目录下添加或更新文档（markdown格式）。

[KomachiSion]

I don't get the reason why add a new api to do metadata?

[Senrian]

Hi @KomachiSion, this PR does not add a new API. It only adds a null check in the existing parseImportDataV2() method. When a ZIP file without .meta.yml/.metadata.yml is uploaded, metaDataItem becomes null and causes NPE at metaDataItem.getItemData(). The fix simply returns an error result with ErrorCode.METADATA_ILLEGAL instead of crashing. No new API is introduced.

[KomachiSion]

Please change the basic branch to develop