move semaphore before opening stream in sendDelta

Author: vyzo

p2p/protocol/identify/peer_loop.go

@@ -115,17 +115,17 @@ func (ph *peerHandler) sendDelta(ctx context.Context) error {
 		return nil
 	}
 
-	ph.ids.pushSemaphore <- struct{}{}
-	defer func() {
-		<-ph.ids.pushSemaphore
-	}()
-
 	// extract a delta message, updating the last state.
 	mes := ph.nextDelta()
 	if mes == nil || (len(mes.AddedProtocols) == 0 && len(mes.RmProtocols) == 0) {
 		return nil
 	}
 
+	ph.ids.pushSemaphore <- struct{}{}
+	defer func() {
+		<-ph.ids.pushSemaphore
+	}()
+
 	ds, err := ph.openStream(ctx, []string{IDDelta})
 	if err != nil {
 		return fmt.Errorf("failed to open delta stream: %w", err)