message: fix: Keep storing sender in ButtplugServer
  If we don't store the sender, embedded clients get stuck because the
  channel closes.
diff: @@ -22,7 +22,7 @@ pub struct ButtplugServer {
  client_spec_version: Option<u32>,
  client_name: Option<String>,
  max_ping_time: u32,
  - // event_sender: Sender<ButtplugMessageUnion>,
  + _event_sender: Sender<ButtplugMessageUnion>,
  }
  impl ButtplugServer {
  @@ -37,7 +37,7 @@ impl ButtplugServer {
  client_name: None,
  client_spec_version: None,
  max_ping_time,
  - // event_sender,
  + _event_sender,
  }
  }
  