text: Title: labelme2coco.py crash when just contines __ignore__ label
  Body: ### Provide environment information
  
  (DET2) D:\FPCs>python --version
  Python 3.9.13
  
  (DET2) D:\FPCs>pip list labelme
  Package                 Version            Editable project location
  ----------------------- ------------------ --------------------------
  labelme                 5.0.5
  
  
  ### What OS are you using?
  
  windows11
  
  ### Describe the Bug
  
  (DET2) D:\FPCs>python D:/DeepLearning/labelme/examples/instance_segmentation/labelme2coco.py --labels classes.txt 000003 labels
  Creating dataset: labels
  Generating dataset from: 000003\dog.json
  Traceback (most recent call last):
    File "D:\DeepLearning\labelme\examples\instance_segmentation\labelme2coco.py", line 209, in <module>
      main()
    File "D:\DeepLearning\labelme\examples\instance_segmentation\labelme2coco.py", line 184, in main
      labels, captions, masks = zip(
  ValueError: not enough values to unpack (expected 3, got 0)
  
  
  ### Expected Behavior
  Skip the label file
  
  ### To Reproduce
  1. Just set __ignore__ label of an image
  2. Create classes.txt file
  3. run labelme2coco.py