序列标注预测数据格式问题

代码位置`easynlp.appzoo.sequence_labeling.predictor.py`
`SequenceLabelingPredictor.preprocess`
```python
text_a = record[self.first_sequence] if self.tokenized else " ".join(record[self.first_sequence])
# record[self.first_sequence] = '中 国 最 棒'
# text_a = '中 国 最 棒' (多加了一个空格)
```
除非指明要预测的序列不包含空格间隔，不然会多一个空格。

Open easynlp.appzoo.sequence_labeling.predictor.py and start with SequenceLabelingPredictor.preprocess. Reproduce the shown input where record[self.first_sequence] is tokenized with spaces and compare the resulting text_a. Done means prediction input does not gain an extra space unless the sequence is explicitly intended to contain space separators.

Written by the indexing model from the issue text.