fix:文件上传后缀不支持大写问题修复

mall-admin/src/main/java/com/suisung/mall/admin/oss/service/impl/OssServiceImpl.java

@@ -105,7 +105,8 @@ public class OssServiceImpl implements OssService {
         // 根据用户获取目录名
         String dir = getUserDirName(user) + DateUtil.format(new Date(), "yyyyMMdd");
         // 创建唯一文件名称
-        String suffix = fileName.substring(fileName.lastIndexOf("."));
+        assert fileName != null;
+        String suffix = fileName.substring(fileName.lastIndexOf(".")).toLowerCase();
         String uploadName = IdUtil.simpleUUID() + suffix;
         String uploadPath = FILEPATH + "/" + dir + "/" + uploadName;