Resolve vanadium/issues#1390
Resolve vanadium/issues#1390

When discover.Advertise returns an error, the "stop" function is nil.
Don't call it.

Change-Id: I04f3c41f180957723afb393a19f5d7dae70132d0

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref