title: Exception when sending message to disconnected client in SignalR
body: <p>In a Hub, I am sending a message to a client using</p>
  
  <pre><code>try { 
      GlobalHost.ConnectionManager.GetHubContext&lt;ContextManagerHub&gt;().Clients.Client(connectionID).SendMessage(message);
  } catch(Exception ex) {
      HandleError(ex);
  }
  </code></pre>
  
  <p>The connectionId is stored using OnConnected and removed using OnDisconnected on the Hub.
  I am a little worried that I am sending messages to disconnected clients, and would like to get exceptions if I do. But the code above never raises exception, even if I try using connectionID = "BAD_ID". Anyone got an idea on how to figure out if the SendMessage actually fails?</p>