Fixed AsyncStreamReaderExtensions.ReadAllAsync argument validation

[gfoidl]

The check for streamReader == null was performed on iterating. With this change the check is performed when getting the IAsyncEnumerable (eager), i.e. when ReadAllAsync is called.

It's an extension method, so it's rather unlikely to be called as null.ReadAllAsync(), but to be on the safe side an fail early I believe this should get in 😉

[thelinuxfoundation]

Thank you for your pull request. Before we can look at your contribution, we need to ensure all contributors are covered by a Contributor License Agreement.

After the following items are addressed, please respond with a new comment here, and the automated system will re-verify.

• User @gfoidl isn't covered by a CLA. They will need to complete the form at https://identity.linuxfoundation.org/projects/cncf

Regards,
CLA GitHub bot

[linux-foundation-easycla]

The committers are authorized under a signed CLA.

• ✅ Günther Foidl (629ea07)

[JamesNK]

Moving the EnumeratorCancellation is interesting. This still works:

var cts = new CancellationTokenSource();

await foreach (var item in call.ResponseStream.ReadAllAsync()
                                              .WithCancellation(cts.Token))
{
    messages.Add(item.Message);

    cts.Cancel();
}

What is suppose to happen if someone specifies both?

var cts1 = new CancellationTokenSource();
var cts2 = new CancellationTokenSource();

await foreach (var item in call.ResponseStream.ReadAllAsync(cts1.Token)
                                              .WithCancellation(cts2.Token))
{
    messages.Add(item.Message);

    cts1.Cancel();
}

[JamesNK]

I tested and it is fine. The state machine honors both.

[gfoidl]

The C#-compiler guys did a brilliant job 👍
Thanks.