Fix knowledge_distillation=False error

[billvsme]

When I was fine-tuning bge-en-icl, I got an error when use --knowledge_distillation False

error like:

[rank0]:     if len(teacher_scores) > 0 and len(passages) > 0:
[rank0]: typeError: object of type 'NoneType' has no len()

I found that the reason is that when knowledge_distillation=False teacher_scores it becomes None.

FlagEmbedding/FlagEmbedding/finetune/embedder/decoder_only/icl/dataset.py

Lines 92 to 100 in 777a9ac

	if self.args.knowledge_distillation:
	if 'pos_scores' in batch_raw_data and batch_raw_data['pos_scores'][i] is not None:
	teacher_scores.append(batch_raw_data['pos_scores'][i][pos_idx])
	for neg_idx in neg_idxs:
	if 'neg_scores' in batch_raw_data and batch_raw_data['neg_scores'][i] is not None:
	teacher_scores.append(batch_raw_data['neg_scores'][i][neg_idx])
	else:
	teacher_scores = None

FlagEmbedding/FlagEmbedding/finetune/embedder/decoder_only/icl/dataset.py

Lines 128 to 129 in 777a9ac

	if len(teacher_scores) > 0 and len(passages) > 0:
	assert len(teacher_scores) == len(passages)