Stop reconnecting websocket after NetworkAdapter.destroy() was called

[chschnell]

Stops NetworkAdapter from reconnecting to its Websocket proxy server after V86 was shut down.

[chschnell]

I came across this when writing a websockproxy server.

When shutting down V86 while using NetworkAdapter, I see at the server side that the WebSocket connection gets closed by the browser.

But a few seconds later the browser creates a new WebSocket connection, even though V86 is off, and this new connection then just sits around idle.

When I restart V86 a new NetworkAdapter instance is created which creates its own WebSocket connection, but the idle connection keeps sitting there.

This PR fixes that by preventing Websocket reconnects after NetworkAdapter.destroy() was called.

[copy]

Nice find, thanks!