Fix: byte array check to fix GetFileDownload function in .NET SDK

[adityaoberai]

What does this PR do?

Corrects the byte array check in the .NET SDK to prevent GetFileDownload/Preview/View functions from returning null values

Test Plan

• Generate new .NET SDK

• Verify correctly generated code in Call() function in Client.cs
  

• Use newly generated .NET SDK with the following C# code

using Appwrite;
using Appwrite.Services;

var client = new Client();
client
    .SetEndpoint("http://cloud.appwrite.io/v1")
    .SetProject("[PROJECT_ID]")
    .SetKey("[API_KEY]");

var storage = new Storage(client);

var download = await storage.GetFileDownload("[BUCKET_ID]t", "[FILE_ID]");

File.WriteAllBytes($"output-{Guid.NewGuid()}.png", download);

Related PRs and Issues

No

Have you read the Contributing Guidelines on issues?

Yes