zmq4: fix REP socket races on client connection

Fixes #119.

Co-authored-by: Sergey Egorov <sergey.egorov@teleste.com>

Author: egorse

rep.go

@@ -114,10 +114,10 @@ func newRepReader(ctx context.Context, state *repState) *repReader {
 }
 
 func (r *repReader) addConn(c *Conn) {
-	go r.listen(r.ctx, c)
 	r.mu.Lock()
 	r.conns = append(r.conns, c)
 	r.mu.Unlock()
+	go r.listen(r.ctx, c)
 }
 
 func (r *repReader) rmConn(conn *Conn) {

socket.go

@@ -280,12 +280,12 @@ func (sck *socket) addConn(c *Conn) {
 		c.Peer.Meta[sysSockID] = uuid
 	}
 	sck.ids[uuid] = c
-	if sck.r != nil {
-		sck.r.addConn(c)
-	}
 	if sck.w != nil {
 		sck.w.addConn(c)
 	}
+	if sck.r != nil {
+		sck.r.addConn(c)
+	}
 	sck.mu.Unlock()
 }