Do not look for segment when there aren't any

This line will crash when there are no masks. This happens for every detect models. We should first look for the type of child. Then decide whether we should look for masks or bbox. This section should become

       # Build valid children
       child_type = results.names[results.boxes.cls[i].cpu().item()]
       child_types.update({child_type: 1})
       if child_type in self.use_segment:
            # Look for segment
       else:
            # look for box