Fix error string not initialized issue.

lib/us/vid_us_data_stream_reader.dart

@@ -22,6 +22,8 @@ class VidUsDataStreamReader {
   late String _errorMsg;
 
   VidUsDataStreamReader(Stream<Uint8List> stream, [int offset = 0]) {
+    _error = false;
+    _errorMsg = '';
     _buffer = Uint8List.fromList(_data).buffer;
     stream.listen(onDataArrived, onError: onStreamError, onDone: onStreamDone);
     _index = offset;