[ONNX] fix size for opset 11 (#35984)
Summary:
Fixing size, as the aten op has updated to support 0 inputs
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35984
Reviewed By: hl475
Differential Revision: D20858214
Pulled By: houseroad
fbshipit-source-id: 8ad0a0174a569455e89da6798eed403c8b162a47
