error message when checkpoint is misspelled

[jsmcibm]

If the retriever checkpoint is nonexistent, the UI message is not helpful.
Note that there is an exception in services

Traceback (most recent call last):
  File "/opt/venv/lib/python3.8/site-packages/grpc/_server.py", line 443, in _call_behavior
    response_or_iterator = behavior(argument, context)
  File "/opt/venv/lib/python3.8/site-packages/primeqa/services/grpc_server/retriever_service.py", line 116, in Retrieve
    retriever_kwargs["checkpoint"] = self._store.get_checkpoint_path(
  File "/opt/venv/lib/python3.8/site-packages/primeqa/services/store.py", line 67, in get_checkpoint_path
    return glob.glob(
IndexError: list index out of range

so the solution may involve changes in that repo also.