PixelShuffle check that output is not null before applying kernel (#85155) (#86262)
* Checks that output tensor is not null before applying kernel in `pixel_shuffle` op
* Checks that output tensor is not null before applying kernel in `pixel_unshuffle` op
* Add test case testing `pixel_shuffle` with shapes producing empty output
* Add test case testing `pixel_unshuffle` with shapes producing empty output
Fixes #85155
FYI @lezcano
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86262
Approved by: https://github.com/lezcano
