Panic on running skywire-visor

[jdknives]

Describe the bug
I get the following panic:

$skywire-mainnet:[dev] skywire-visor 
[2020-06-23T18:10:31+02:00] DEBUG []: Process info delay=0s parent_systemd=false systemd=false
Version "v0.2.3-402-ge4df4494" built on "2020-06-23T16:08:21Z" against commit "e4df44941138f4adb1fa5aff3f82cd9465d76de3"
[2020-06-23T18:10:31+02:00] INFO [visor:config]: Reading config from file. filepath="skywire-config.json"
[2020-06-23T18:10:31+02:00] INFO [visor:config]: Flushing config to file. config_version="v1.0.0" filepath="skywire-config.json"
[2020-06-23T18:10:31+02:00] INFO [visor:startup]: Begin startup. public_key=026715be519cd0c3d42ae63e25c41f6715785f9c5cd7bf43ecf2057bccd0a0bb69
[2020-06-23T18:10:31+02:00] INFO [1/10] [visor:startup:updater]: Starting module...
[2020-06-23T18:10:31+02:00] INFO [1/10] [visor:startup:updater]: Module started successfully. elapsed=72.096µs
[2020-06-23T18:10:31+02:00] INFO [2/10] [visor:startup:eventbroadcaster]: Starting module...
[2020-06-23T18:10:31+02:00] INFO [2/10] [visor:startup:eventbroadcaster]: Module started successfully. elapsed=15.121µs
[2020-06-23T18:10:31+02:00] INFO [3/10] [visor:startup:snet]: Starting module...
[2020-06-23T18:10:32+02:00] INFO [snet.dmsgC]: Discovering dmsg servers...
[2020-06-23T18:10:32+02:00] INFO [snet.stcpC]: listening on tcp addr: 192.168.55.88:7777
[2020-06-23T18:10:32+02:00] INFO [snet.sudpC]: listening on udp addr: [::]:7787
[2020-06-23T18:10:32+02:00] INFO [snet.dmsgC]: Connecting to the dmsg network... timeout=20s
[2020-06-23T18:10:33+02:00] INFO [snet.dmsgC]: Dialing session... remote_pk=02a49bc0aa1b5b78f638e9189be4ed095bac5d6839c828465a8350f80ac07629c0
[2020-06-23T18:10:33+02:00] INFO [snet]: successfully connected to address resolver
[2020-06-23T18:10:33+02:00] INFO [snet.stcprC]: listening on tcp addr: [::]:7778
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x40 pc=0x44e56ce]

goroutine 30 [running]:
github.com/SkycoinProject/skywire-mainnet/pkg/snet/stcph.(*Client).Serve(0xc00013b860, 0xc00013b860, 0x4188f67)
	/Users/work/go/src/github.com/SkycoinProject/skywire-mainnet/pkg/snet/stcph/client.go:79 +0x6e
github.com/SkycoinProject/skywire-mainnet/pkg/snet.(*Network).Init.func2(0xc0000f64d0)
	/Users/work/go/src/github.com/SkycoinProject/skywire-mainnet/pkg/snet/network.go:350 +0x6f
created by github.com/SkycoinProject/skywire-mainnet/pkg/snet.(*Network).Init
	/Users/work/go/src/github.com/SkycoinProject/skywire-mainnet/pkg/snet/network.go:343 +0x1da

This happens after running skywire visor on develop with stcpr defined in the config. As soon as it is removed, the panic disappears.

Steps to Reproduce

1. Generate a config from develop branch.
2. Run skywire-visor

[evanlinjin]

Should be fixed by #415