Make TestFile Image threadsafe.

[JimBobSquarePants]

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Description

Fix #2178

CC @br3aker

[br3aker]

Well, we can do a double check lock instead so image would never be loaded twice:

// this.image should be marked volatile still
if (this.image is null)
{
    lock (this.lockObject)
    {
        if (this.image is null)
        {
            this.image = ImageSharp.Image.Load<Rgba32>(this.Bytes);
        }
    }
}
return this.image;

I proposed Interlocked solution, I know, but lock solution is a lot more readable IMO and doesn't have a possible flaw of loading the same image twice. It's also isn't slow on reads due to locking as most of the time first if check would be true.

Maybe we should use it instead due to simplicity?

[JimBobSquarePants]

Definitely far more readable. I’m happy to switch out

[br3aker]

Suggested change

	private readonly object syncLock;
	private readonly object syncLock = new();

[JimBobSquarePants]

Ha! Can't believe I missed that!