Consider adding error handling to the samples

[vicancy]

Currently we have something like:

public async Task MyRestCallHandler{
var result = await CalcResult();
await hub.Clients.SendAsync(...);
return result;
}

And if I don't wrap call to the hub into try-catch, the client gets 500 error, although the operation was generally ok. Sometimes client is an automated test which fails and gives a false alarm. All samples I find do not care for exceptions handling when contacting signalr.