Azure Queue Storage check fails if queue name is not provided

[ben-m-lucas]

There is a bug in AzureHealthCheckBuilderExtensions.AddAzureQueueStorageCheck where the health check fails if a queue name is not provided because it attempts to get a table with a "null" name.

Likewise, if the name is passed in, the health check fails to actually check that the table exists.

Lines 153-158 currently read:

                    if (String.IsNullOrWhiteSpace(queueName))
                    {
                        var queue = queueClient.GetQueueReference(queueName);

                        result = await queue.ExistsAsync();
                    }

Line 153 should be:
if (!String.IsNullOrWhiteSpace(queueName))