Pre-existing labels do not get imported

Describe the bug Pre-existing labels will not be imported if the file extension differs from the file extension of the corresponding image.

To Reproduce Steps to reproduce the behavior:

1. Put example image file in /data, i.e. /data/patient_0001.dcm
2. Put example label file in /data/labels/final, that has another file extensions, i.e. /data/labels/final/patient_0001.nii.gz
3. Start monailabel server to initiate file parsing/import procedure, monailabel start_server --app app --studies /data
4. Pre-existing label file is not imported, server log shows the following:

[2021-12-10 08:55:32,700] [436] [MainThread] [INFO] (monailabel.datastore.local:125) - Auto Reload: True; Extensions: ['*.dcm', '*.nii.gz', '*.nii', '*.nrrd']
[2021-12-10 08:55:32,711] [436] [MainThread] [INFO] (monailabel.datastore.local:551) - Adding New Image: patient_0001 => patient_0001.dcm
[2021-12-10 08:55:32,759] [436] [MainThread] [INFO] (monailabel.datastore.local:581) - Adding New Label: final => patient_0001 => patient_0001.nii.gz
[2021-12-10 08:55:32,763] [436] [MainThread] [ERROR] (uvicorn.error:89) - Traceback (most recent call last):
  File "/opt/conda/lib/python3.8/site-packages/starlette/routing.py", line 540, in lifespan
    async for item in self.lifespan_context(app):
  File "/opt/conda/lib/python3.8/site-packages/starlette/routing.py", line 481, in default_lifespan
    await self.startup()
  File "/opt/conda/lib/python3.8/site-packages/starlette/routing.py", line 516, in startup
    await handler()
  File "/opt/conda/lib/python3.8/site-packages/monailabel/app.py", line 99, in startup_event
    instance = app_instance()
  File "/opt/conda/lib/python3.8/site-packages/monailabel/interfaces/utils/app.py", line 51, in app_instance
    app = c(app_dir=app_dir, studies=studies, conf=conf)
  File "/workspace/code/main.py", line 43, in __init__
    super().__init__(
  File "/opt/conda/lib/python3.8/site-packages/monailabel/interfaces/app.py", line 85, in __init__
    self._datastore: Datastore = self.init_datastore()
  File "/opt/conda/lib/python3.8/site-packages/monailabel/interfaces/app.py", line 136, in init_datastore
    return LocalDatastore(
  File "/opt/conda/lib/python3.8/site-packages/monailabel/datastore/local.py", line 142, in __init__
    self._reconcile_datastore()
  File "/opt/conda/lib/python3.8/site-packages/monailabel/datastore/local.py", line 530, in _reconcile_datastore
    invalidate += self._add_non_existing_labels(tag)
  File "/opt/conda/lib/python3.8/site-packages/monailabel/datastore/local.py", line 586, in _add_non_existing_labels
    "checksum": file_checksum(os.path.join(self._datastore.image_path(), name)),
  File "/opt/conda/lib/python3.8/site-packages/monailabel/utils/others/generic.py", line 112, in file_checksum
    with open(file, "rb") as content:
FileNotFoundError: [Errno 2] No such file or directory: '/workspace/data/./patient_0001.nii.gz'

[2021-12-10 08:55:32,763] [436] [MainThread] [ERROR] (uvicorn.error:35) - Application startup failed. Exiting.

Expected behavior Pre-existing label file should get imported although the file extension differs from the file extension of the corresponding image.

Proposed solution Change line 586 in MONAILabel/monailabel/datastore/local.py

"checksum": file_checksum(os.path.join(self._datastore.label_path(), name)),`

self._datastore.image_path() may be changed to self._datastore.label_path()

Should I create a pull request?

Environment docker: projectmonai/monailabel

python -c 'import monai; monai.config.print_debug_info()'

================================
Printing MONAI config...
================================
MONAI version: 0.8.0+4.g8a1454a7
Numpy version: 1.21.2
Pytorch version: 1.10.0a0+0aef44c
MONAI flags: HAS_EXT = True, USE_COMPILED = False
MONAI rev id: 8a1454a75de71ee50099d0302ce5146c900cee09

Optional dependencies:
Pytorch Ignite version: 0.4.6
Nibabel version: 3.2.1
scikit-image version: 0.18.3
Pillow version: 8.4.0
Tensorboard version: 2.6.0
gdown version: 4.2.0
TorchVision version: 0.11.0a0
tqdm version: 4.62.3
lmdb version: 1.2.1
psutil version: 5.8.0
pandas version: 1.3.4
einops version: 0.3.2
transformers version: 4.12.5
mlflow version: 1.21.0

For details about installing the optional dependencies, please visit:
    https://docs.monai.io/en/latest/installation.html#installing-the-recommended-dependencies


================================
Printing system config...
================================
System: Linux
Linux version: Ubuntu 20.04.3 LTS
Platform: Linux-5.10.76-linuxkit-x86_64-with-glibc2.10
Processor: x86_64
Machine: x86_64
Python version: 3.8.12
Process name: python
Command: ['python', '-c', 'import monai; monai.config.print_debug_info()']
Open files: []
Num physical CPUs: 2
Num logical CPUs: 2
Num usable CPUs: 2
CPU usage (%): [7.3, 25.3]
CPU freq. (MHz): 3200
Load avg. in last 1, 5, 15 mins (%): [14.5, 30.0, 34.0]
Disk usage (%): 46.1
Avg. sensor temp. (Celsius): UNKNOWN for given OS
Total physical memory (GB): 1.9
Available memory (GB): 1.1
Used memory (GB): 0.4

================================
Printing GPU config...
================================
Num GPUs: 0
Has CUDA: False
cuDNN enabled: True
cuDNN version: 8204

[jlvahldiek]

Just raised PR #557. Could be closed. Thank you.

[SachidanandAlle]

Please feel free to raise a PR… at the end… its all open source