Fix the Unreal Plugin's GetGameServer

[dotcom]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug

/kind cleanup
/kind documentation
/kind feature
/kind hotfix

What this PR does / Why we need it:

The fix is extremely simple.

first commit :
I think the point where OnProcessRequestComplete().BindLambda() after SendRequest() is done needs to be fixed.(In GetGameServer())
https://github.com/googleforgames/agones/compare/master...dotcom:master?diff=split#diff-80dbe36c10c363357ae5c22ced334ea2L151

For implementers who want to add more processing to the Request, I have split the processing.

second commit:
We should check whether the request is acceptable or not with EHttpResponseCodes::IsOk

Once review has occurred, please rebase your PR down to a single commit. This will ensure a nice clean Git history.

I'm separating the commits for two different fixes, but squash them as needed.

I'd like further comments from people who are familiar with UE4.

Thank you.

[agones-bot]

Build Succeeded 👏

Build Id: c61d9100-9ab1-4eae-84b2-8bc007efaf3f

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.6.0-8d5fc95
• image: gcr.io/agones-images/agones-sdk:1.6.0-8d5fc95
• image: gcr.io/agones-images/agones-ping:1.6.0-8d5fc95
• Linux C++ SDK (build): agonessdk-1.6.0-8d5fc95-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-8d5fc95.zip

A preview of the website (the last 30 builds are retained):

• https://8d5fc95-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1581/head:pr_1581 && git checkout pr_1581
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-8d5fc95

[WVerlaek]

LGTM, interesting that the order of BindLambda needed to change, I don't think we noticed any issues there. But the changes look sensible, especially checking the response code for errors

[dotcom]

@WVerlaek
Thank you for checking.
BindLambda after SendRequest seems to register the callback after execution, but I think it's safe when HttpThread works as a FSingleThreadRunnable. (This would be handled when Tick in the HttpThread is called.) However, in the case of FRunnable, I think this is not safe. (Please correct me if I'm wrong.)
But I'm not sure where it actually has a branch to treat HttpThread as FSingleThreadRunnable or FRunnable.

[roberthbailey]

@markmandel - how do you feel about squeezing in this bug fix right before the release cut?

[markmandel]

@markmandel - how do you feel about squeezing in this bug fix right before the release cut?

SGTM, let's do it.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dotcom, markmandel

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