Followup fix for Custom AR V2 in non NVL scenarios (#24742)

Co-authored-by: b8zhong <b8zhong@users.noreply.github.com>

python/sglang/srt/distributed/device_communicators/custom_all_reduce_v2.py

@@ -93,12 +93,14 @@ class CustomAllReduceV2:
 
     @contextmanager
     def capture(self):
+        if self.disabled:
+            yield
+            return
         try:
             self.obj.set_cuda_graph_capture(True)
             yield
         finally:
             self.obj.set_cuda_graph_capture(False)
-        if not self.disabled:
         # cannot call when graph is capturing
         assert (
             torch.cuda.is_current_stream_capturing() == False