Need to check HubConnectionState for calls to Invoke

[mikaelm12]

Before calling methods that require the HubConnection to be connected we run a simple connection state check like
https://github.com/aspnet/AspNetCore/blob/e310ccac7b30e901f657f81c86c4048fecfedf7b/src/SignalR/clients/java/signalr/src/main/java/com/microsoft/signalr/HubConnection.java#L464-L466

We don't have this check for the invoke method.

[mikaelm12]

This was approved for the 2.2.2 patch

[mikaelm12]

@natemcmaster When will 2.2.2 open for changes?

[natemcmaster]

Tentatively, later this week. I'll send email to the team when the branch opens up.

[mikaelm12]

Merged into 2.2.2 and master now
#4400