WebSockets: closed signal not emitted when io stream is SoupIOStream

That's the case of connections created by SoupSession. In that case, if
the server hasn't closed its end of the connection, we fail to shutdown
the client end, because shutdown_wr_io_stream() does nothing when the io
stream is not a GSocketConnection. So, for SoupIOStream we need to get
the base io stream which is a GSocketConnection.
1 job for carlosgc/websockets-soup-io-stream-shutdown in 49 seconds (queued for 3 seconds)
Status Job ID Name Coverage
passed #336874