Hotfix-6.0.8 CircularBuffer throws exception

[SeanFeldman]

Who's affected

Anyone who's using Azure Service Bus transports and using Bus.Send() or Bus.Publish() in a very tight loop with multiple threads.

Symptoms

Due to a calculation error that can happen with concurrent access an IndexOutOfRangeException exception can be thrown

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Reported in GG: https://groups.google.com/forum/#!topic/particularsoftware/a1GigfXhI94

CircularBuffer.Get() is not thread safe and may throw exception when used in concurrent mode

Repro:

Parallel.ForEach(hugeArray, new ParallelOptions() { MaxDegreeOfParallelism = 5 }, item =>
{
    Bus.Send(new SomethingCommand
    {
        Item = item
    });
});

Connects to Particular/NServiceBus.AzureServiceBus#59