Get data path of initial stream, not "use config from" stream

bob/io/stream/stream_file.py

@@ -102,9 +102,9 @@ class StreamFile:
     # load stream data
     def load_stream_data(self, stream_name, index):
         data_config = self.get_stream_config(stream_name)
+        data_path = data_config["path"]
         if "use_config_from" in data_config:
             data_config = self.get_stream_config(data_config["use_config_from"])
-        data_path = data_config["path"]
 
         # load only relevant data
         if isinstance(index, int):