test: avoid double chan close in integration testing framework

networktest.go

@@ -271,20 +271,20 @@ func (l *lightningNode) Stop() error {
 	// - start of the node wasn't initiated
 	// - process wasn't spawned
 	// - process already finished
-
 	select {
+	case <-l.quit:
+		return nil
 	case <-l.processExit:
 		return nil
 	default:
-		close(l.quit)
-		l.wg.Wait()
+	}
 
+	close(l.quit)
 	if runtime.GOOS == "windows" {
 		return l.cmd.Process.Signal(os.Kill)
 	}
 	return l.cmd.Process.Signal(os.Interrupt)
 }
-}
 
 // Restart attempts to restart a lightning node by shutting it down cleanly,
 // then restarting the process. This function is fully blocking. Upon restart,