[Bug]: single lora request error make all processing requests error

[jinzhen-lin]

Your current environment

The output of `python collect_env.py`

🐛 Describe the bug

Vllm load lora checkpoints when executing model

https://github.com/vllm-project/vllm/blob/v0.4.2/vllm/worker/model_runner.py#L789-L790

https://github.com/vllm-project/vllm/blob/v0.4.2/vllm/lora/worker_manager.py#L138-L172

Then when we get an error when loading lora checkpoint (e.g. lora rank > max_lora_rank), all processing requests would fail (no matter whether other requests use lora).