Fix/vpn panic

[ersonp]

Did you run make format && make check?

Fixes #885

Changes:

• Moved remoteClosed chan check from select to if.

How to test this PR:

1. Use the following services

dmsg_discovery: http://dmsg.discovery.skywire.cc
transport_discovery: http://transportt.skywire.cc
address_resolver: http://boom.skywire.cc
setup_node: 026c2a3e92d6253c5abd71a42628db6fca9dd9aa037ab6f4e3a31108558dfd87cf
route_finder: http://rft.skywire.cc
uptime_tracker: http://uptime.tracker.skywire.cc
service_discovery: http://sdt.skywire.cc

2. Run visorA with a vpn-server
3. On visorB make a dmsg transport to visorA. Will have to make one via cli or perisitent_transports as UI needs to be rebuilt

• cli

./skywire-cli visor add-tp <visor-a-pk> --type dmsg 

• perisitent_transports in config add

"persistent_transports": [
		{
			"pk": "<visor-a-pk>",
			"type": "dmsg"
		}
],

4. Add pk of visorA to VPN client and start it.
5. Start a video in the background and stop the VPN client.
6. There should be no panic.