fix(srt): check if sample_indices is not None before usage. (#5633)

Author: aoshen524

python/sglang/srt/layers/logits_processor.py

@@ -335,13 +335,13 @@ def forward(
                     aux_pruned_states = torch.cat(aux_pruned_states, dim=-1)
                     hidden_states_to_store = (
                         aux_pruned_states[sample_indices]
-                        if sample_indices
+                        if sample_indices is not None
                         else aux_pruned_states
                     )
                 else:
                     hidden_states_to_store = (
                         pruned_states[sample_indices]
-                        if sample_indices
+                        if sample_indices is not None
                         else pruned_states
                     )
             else: