fft: Fix invalid shape error for complex-to-real transforms (#73012)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/72910
`last_dim_size` is the expected output size for the
Hermitian-compressed dimension and must be > 0. The confusingly named
`ld` represents the input's last dim size which is calculated as
`last_dim_size / 2 + 1` so could never be 0.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73012
Reviewed By: ngimel
Differential Revision: D34387147
Pulled By: mruberry
fbshipit-source-id: 6b410088efe2a9e117a5c6d8beefda370363dbb0
(cherry picked from commit f8d771ed3645efa5e00e8a73e390f280aa664309)
