IndexOutOfRangeException in DisconnectedPerformanceMonitor.PulseAsync()

I'm periodically calling DisconnectedPerformanceMonitor.PulseAsync() to collect statistics on my TaskHubs.

Every now and then I encounter an IndexOutOfRange exception with the following stack:

```
ClientCommandRequest: Details=System.IndexOutOfRangeException: Index was outside the bounds of the array.
at DurableTask.AzureStorage.Monitoring.DisconnectedPerformanceMonitor.QueueMetricHistory.Add(Int32 value) in /_/src/DurableTask.AzureStorage/Monitoring/DisconnectedPerformanceMonitor.cs:line 558
at DurableTask.AzureStorage.Monitoring.DisconnectedPerformanceMonitor.d__29.MoveNext() in /_/src/DurableTask.AzureStorage/Monitoring/DisconnectedPerformanceMonitor.cs:line 188
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at DurableTask.AzureStorage.Monitoring.DisconnectedPerformanceMonitor.d__28.MoveNext() in /_/src/DurableTask.AzureStorage/Monitoring/DisconnectedPerformanceMonitor.cs:line 138
--- End of stack trace from previous location where exception was thrown ---
...
```

This looks like a race condition somewhere.