Deadlock when stopping a hubConnection if the WebSocket did not start

[moozzyk]

This test consistently reproduces the @datwelk's issue:

    func testThatDeadlockDoesNotHappen() {
        let didStop = expectation(description: "connection stopped")
        let hubConnectionDelegate = TestHubConnectionDelegate()
        hubConnectionDelegate.connectionDidCloseHandler = { error in
            XCTAssertNil(error)
            didStop.fulfill()
        }

        let hubConnection = HubConnectionBuilder(url: URL(string: "\(BASE_URL)/testhub")!)
            .withLogging(minLogLevel: .debug)
            .withHubConnectionDelegate(delegate: hubConnectionDelegate)
            .withHttpConnectionOptions(configureHttpOptions: {options in
                options.skipNegotiation = true
            })
            .build()
        hubConnection.start()
        hubConnection.stop()

        waitForExpectations(timeout: 5 /*seconds*/)
    }

stop is blocked on waiting for start to complete:

SignalR-Client-Swift/Sources/SignalRClient/HttpConnection.swift

Line 203 in 3ea5fae

self.startDispatchGroup.wait()

start cannot complete because neither of open, error, close events were fired because they want to by default run on the main thread as per:

SignalR-Client-Swift/Sources/SignalRClient/WebSocket.swift

Line 1733 in 3ea5fae

/// The queue for firing off events. default is main_queue