[JIT] fix unfold shape analysis (#40749)
Summary:
unfold on a 0-dimensioned tensor returns a 1-dim tensor
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40749
Differential Revision: D22361481
Pulled By: eellison
fbshipit-source-id: 621597e5f97f6e39953eb86f8b85bb4142527a9f
