Fix LLMEngine.del dp_group cleanup condition (#29954)

Signed-off-by: Yongtao Huang <[email protected]>

Author: hyongtao-code

vllm/v1/engine/llm_engine.py

@@ -409,8 +409,6 @@ def apply_model(self, func: Callable[[nn.Module], _R]) -> list[_R]:
         return self.collective_rpc("apply_model", args=(func,))
 
     def __del__(self):
-        if (
-            dp_group := getattr(self, "dp_group", None)
-            and not self.external_launcher_dp
-        ):
+        dp_group = getattr(self, "dp_group", None)
+        if dp_group is not None and not self.external_launcher_dp:
             stateless_destroy_torch_distributed_process_group(dp_group)