[cohere][fix][spec-decode]: fix crash when allowed_token_ids is set without penalties (#35654)

Signed-off-by: kkt-cohere <komal@cohere.com>

vllm/v1/sample/rejection_sampler.py

@@ -271,7 +271,7 @@ class RejectionSampler(nn.Module):
 
         # Calculate indices of target logits.
         if sampling_metadata.allowed_token_ids_mask is not None or has_penalties:
-            num_requests = len(sampling_metadata.output_token_ids)
+            num_requests = len(metadata.num_draft_tokens)
             num_draft_tokens = torch.tensor(metadata.num_draft_tokens, device="cpu")
             original_indices = torch.arange(num_requests, device="cpu")
             repeat_indices_cpu = original_indices.repeat_interleave(num_draft_tokens)