throw error if library path is not found in get_db_file

corrlib/tools.py

@@ -115,6 +115,8 @@ def get_db_file(path: Path) -> Path:
     db_file: str
         The file holding the database.
     """
+    if not os.path.exists(path):
+        raise FileNotFoundError(f"Corrlib path {path} does not exist.")
     config_path = os.path.join(path, CONFIG_FILENAME)
     config = ConfigParser()
     if os.path.exists(config_path):