nip77: fix one possible infinite loop with channels.

nip77/nip77.go

@@ -128,17 +128,27 @@ func NegentropySync(
 		})
 	}
 
+	done := make(chan struct{})
 	go func() {
+		defer close(done)
 		wg.Wait()
-		errch <- nil
+		select {
+		case errch <- nil:
+		case <-ctx.Done():
+		}
 	}()
 
-	err = <-errch
+	select {
+	case err = <-errch:
 		if err != nil {
 			return err
 		}
-
 		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-done:
+		return nil
+	}
 }
 
 func SyncEventsFromIDs(ctx context.Context, dir Direction) {