[Bugfix] fix V1 Engine crash while handling requests with duplicate request id (#15043)

Signed-off-by: Jiahui Sun <jhsun2020@gmail.com>

vllm/v1/engine/core.py

@@ -179,16 +179,6 @@ class EngineCore:
                 scheduler_stats=self.scheduler.make_stats(),
             )
         scheduler_output = self.scheduler.schedule()
-
-        # This case may occur when the only unfinished requests are
-        # structured output requests where the grammar has not finished
-        # compiling yet, so there's nothing to run.
-        if scheduler_output.total_num_scheduled_tokens == 0:
-            return EngineCoreOutputs(
-                outputs=[],
-                scheduler_stats=self.scheduler.make_stats(),
-            )
-
         output = self.model_executor.execute_model(scheduler_output)
         engine_core_outputs = self.scheduler.update_from_output(
             scheduler_output, output)  # type: ignore