[Bugfix] Fix potential EAGLE spec decode segfault during graph capture (#32818)

Signed-off-by: Matthew Wong <Matthew.Wong2@amd.com>

vllm/v1/spec_decode/eagle.py

@@ -1222,10 +1222,14 @@ class SpecDecodeBaseProposer:
                 num_tokens_dp_padded, num_tokens_across_dp = self._pad_batch_across_dp(
                     num_tokens_unpadded=num_tokens, num_tokens_padded=num_tokens
                 )
-                cudagraph_runtime_mode, batch_desc = self.cudagraph_dispatcher.dispatch(
-                    num_tokens_dp_padded
+                if use_cudagraphs:
+                    cudagraph_runtime_mode, batch_desc = (
+                        self.cudagraph_dispatcher.dispatch(num_tokens_dp_padded)
                     )
                     num_input_tokens = batch_desc.num_tokens
+                else:
+                    cudagraph_runtime_mode = CUDAGraphMode.NONE
+                    num_input_tokens = num_tokens_dp_padded
                 if num_tokens_across_dp is not None:
                     num_tokens_across_dp[self.dp_rank] = num_input_tokens