title: RestSharp "Invalid JSON string" when connection lost
body: <p>Is there a way to see when RestClient.ExecuteAsync() fails because of a lost connection?</p>
  
  <p>When I cut off the network connection, the response contains a SerializationException "Invalid JSON String", as if it received content that could not be parsed. I would instead expect an exception related to the network connection, like some sort of IOException for example.</p>
  
  <p>For now I might assume that if ContentLength==0 then the response wasn't actually a response but rather a lack of connection, so that I can report the appropriate error to the user and suggest they check their Internet connection.</p>