Description

When using CrossEncoderRanker as a ranker for EmbeddingRetrieve, calling the rank function of CrossEncoderRanker results in an "index out of bounds" error when the length of the retrieved results is 0.
Close #1523

How Has This Been Tested?

ranker = CrossEncoderRanker(topk=3, model=os.path.join(MODEL_PATH, rerank_model))
ranker.rank(candidates_with_scores=[], query="what happened")

Snapshots:

Checklist:

• My code follows the style guidelines of this project
• I have already rebased the commits and make the commit message conform to the project standard.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules