Disconnect from servers on shutdown

main.go

@@ -64,6 +64,8 @@ func main() {
 					cc.Close()
 				}
 
+				<-cc.server().Closed()
+				cc.srv = nil
 				wg.Done()
 			}()
 		}

server_conn.go

@@ -80,6 +80,7 @@ func handleSrv(sc *serverConn) {
 					case <-sc.client().Closed():
 					case <-ack:
 						sc.client().Close()
+						sc.client().srv = nil
 						sc.clt = nil
 					}
 				}