[Bugfix] Prevent IndexError for cached requests when pipeline parallelism is disabled (#20486)

Signed-off-by: Peter Pan <Peter.Pan@daocloud.io>

vllm/v1/core/sched/scheduler.py

@@ -635,6 +635,8 @@ class Scheduler(SchedulerInterface):
                 token_ids = req.all_token_ids[req.num_computed_tokens:req.
                                               num_computed_tokens + num_tokens]
                 new_token_ids.append(token_ids)
+            else:
+                new_token_ids.append([])
             new_block_ids.append(req_to_new_block_ids[req_id])
             num_computed_tokens.append(req.num_computed_tokens)
         # Because resumed_reqs is usually empty, it is more efficient to do