ONNX: fix default function value in _optimize_graph (#83996)
The default value for params_dict in _optimize_graph, which is None, throw the following error:
> _C._jit_pass_onnx_unpack_quantized_weights(
> TypeError: _jit_pass_onnx_unpack_quantized_weights(): incompatible function arguments. The following argument types are supported:
> 1. (arg0: torch::jit::Graph, arg1: Dict[str, IValue], arg2: bool) -> Dict[str, IValue]
Replacing it by an empty dict fixes the issue (and makes more sense).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83996
Approved by: https://github.com/BowenBao
