消除部分warning

common/Tnb.Common/Security/FileHelper.cs

@@ -505,6 +505,7 @@ public class FileHelper
 
     #endregion
 
+#pragma warning disable CA1416 // 验证平台兼容性
     #region 生成高清晰缩略图
 
     /// <summary>
@@ -669,6 +670,7 @@ public class FileHelper
     }
 
     #endregion
+#pragma warning restore CA1416 // 验证平台兼容性
 
     #region  将文件路径转为内存流
 
@@ -712,7 +714,8 @@ public class FileHelper
 
         if (selectFiles.Count > 0)
         {
-            return selectFiles.FirstOrDefault().FullName;
+            //modified by PhilPan 
+            return selectFiles.First().FullName;
         }
 
         return Path.Combine(folderPath, $@"{prefix}_{DateTime.Now.ParseToUnixTime()}.log");
@@ -737,7 +740,7 @@ public class FileHelper
                 Microsoft.AspNetCore.Http.HttpContext? httpContext = App.HttpContext;
                 httpContext.Response.ContentType = "application/octet-stream";
                 httpContext.Response.Headers.Add("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(fileName, Encoding.UTF8));
-                httpContext.Response.Headers.Add("Content-Length", buff.Length.ToString());
+                httpContext.Response.Headers.Add("Content-Length", buff?.Length.ToString());
                 httpContext.Response.Body.WriteAsync(buff);
                 httpContext.Response.Body.Flush();
                 httpContext.Response.Body.Close();