rpc: wrap canceling a breach watch in a select case

rpcserver.go

@@ -613,7 +613,11 @@ func (r *rpcServer) CloseChannel(in *lnrpc.CloseChannelRequest,
 			r.server.htlcSwitch.RemoveLink(chanID)
 		}
 
-		r.server.breachArbiter.settledContracts <- chanPoint
+		select {
+		case r.server.breachArbiter.settledContracts <- chanPoint:
+		case <-r.quit:
+			return fmt.Errorf("server shutting down")
+		}
 
 		// With the necessary indexes cleaned up, we'll now force close
 		// the channel.

server.go

@@ -165,6 +165,7 @@ func newServer(listenAddrs []string, chanDB *channeldb.DB, cc *chainControl,
 	s.htlcSwitch = htlcswitch.New(htlcswitch.Config{
 		LocalChannelClose: func(pubKey []byte,
 			request *htlcswitch.ChanClose) {
+
 			s.peersMtx.RLock()
 			peer, ok := s.peersByPub[string(pubKey)]
 			s.peersMtx.RUnlock()