do not fallback on ncurses input on Cancel

cmd/liber/liber.go

@@ -109,15 +109,16 @@ func promptUserDialog(path string, choices []*liber.Metadata) (*liber.Metadata,
 		args = append(args, strconv.Itoa(idx+1))
 		args = append(args, md.String())
 	}
-	log.Printf("running: %s %v", dialog, args)
 	var output bytes.Buffer
 	cmd := exec.Command(dialog, args...)
 	cmd.Stdin = os.Stdin
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = &output
 	if err := cmd.Run(); err != nil {
+		// If the user selects 'Cancel', dialog will exit with
+		// status 1.
 		log.Printf("dialog failed: %v", err)
-		return nil, err
+		return nil, nil
 	}
 	result, err := strconv.Atoi(strings.TrimSpace(output.String()))
 	if err != nil {