enable empty batch for all flavor of convolutions (#32709)
Summary:
resubmitting https://github.com/pytorch/pytorch/issues/32612 after a merge gone wrong. Enables convolution with an empty batch or number of channels for all flavors of convolution (grouped convolution, convTranspose). Would make https://github.com/pytorch/pytorch/issues/31658 unnecessary. Also returns zero gradients for the parameters, that's necessary for correct DDP operation.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32709
Differential Revision: D19627968
Pulled By: ngimel
fbshipit-source-id: 7359759bd05ff0df0eb658cac55651c607f1b59f
