Fix issue with moe trace generation

[daweilics]

Without the fix, we get the following failure when generating moe traces:

MoE model: Converting Chakra
processing zero rank before cross bucket ((pp, 0), (ep, 0), (cp, 0), (tp, 0), (dp, 0))
Traceback (most recent call last):
  File "/home/dli/workspace/symbolic_tensor_graph/main.py", line 568, in <module>
    main()
    ~~~~^^
  File "/home/dli/workspace/symbolic_tensor_graph/main.py", line 478, in main
    distributed_chakra_graph_moe = BundledConvertChakra.apply(
        distributed_tensor_graph_moe,
    ...<2 lines>...
        mixed_precision=args.mixed_precision,
    )
  File "/home/dli/workspace/symbolic_tensor_graph/symbolic_tensor_graph/graph/convert_chakra.py", line 634, in apply
    tensor_map_nodes = cls._ConvertChakra.apply_before_cross_bucket_comms(
        tensor_graph, symbol_map_value, bundled_graph.spatial_parallel_dims
    )
  File "/home/dli/workspace/symbolic_tensor_graph/symbolic_tensor_graph/graph/convert_chakra.py", line 500, in apply_before_cross_bucket_comms
    nodes_this_tensor = cls._tensor_to_nodes(
        tensor, symbol_map_value, spatial_parallel_syms
    )
  File "/home/dli/workspace/symbolic_tensor_graph/symbolic_tensor_graph/graph/convert_chakra.py", line 258, in _tensor_to_nodes
    cls._insert_comp(tensor, symbol_map_value, nodes_this_tensor)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dli/workspace/symbolic_tensor_graph/symbolic_tensor_graph/graph/convert_chakra.py", line 68, in _insert_comp
    tensor_ops = Tensor.eval_expr(tensor.ops, symbol_map_value)
  File "/home/dli/workspace/symbolic_tensor_graph/symbolic_tensor_graph/tensor.py", line 114, in eval_expr
    target_eval_expr_cache[expr] = float(
                                   ~~~~~^
        expr.evalf(subs=target_symbol_value_dict)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/dli/miniconda3/lib/python3.13/site-packages/sympy/core/expr.py", line 375, in __float__
    raise TypeError("Cannot convert expression to float")
TypeError: Cannot convert expression to float

With the fix, we can generate moe traces fine.

I think this block of code is not supposed to be run. As suggested by the context, it should just belong to the else branch. Let me know if this is a valid fix.