Fix error due to CustomAllreduce setup failure (#4815)

Signed-off-by: Kebe <mail@kebe7jun.com>

python/sglang/srt/distributed/parallel_state.py

@@ -264,10 +264,16 @@ class GroupCoordinator:
         self.ca_comm: Optional[CustomAllreduce] = None
         if use_custom_allreduce and self.world_size > 1:
             # Initialize a custom fast all-reduce implementation.
-            self.ca_comm = CustomAllreduce(
-                group=self.cpu_group,
-                device=self.device,
-            )
+            try:
+                self.ca_comm = CustomAllreduce(
+                    group=self.cpu_group,
+                    device=self.device,
+                )
+            except Exception as e:
+                logger.warning(
+                    f"Setup Custom allreduce failed with {e}. To silence this "
+                    "warning, specify --disable-custom-all-reduce explicitly."
+                )
 
         from sglang.srt.distributed.device_communicators.hpu_communicator import (
             HpuCommunicator,