fix: ExternalLoRA node Make downloaded files reusable

[GwonHyeok]

if lora_save_name in existing_loras:
                    raise "LoRA file '{lora_save_name}' already exists."

This code is raising an error if default_lora_name starts with http and the file lora_save_name already exists.

This implementation needs to add a part to check if the file has been downloaded externally.

Instead of raising an error, it would be better to use return (lora_save_name,) to make the saved file available.