Fix empty shape inference for ConvTranspose2d
Fix empty shape inference for ConvTranspose2d

Summary: This fixes the empty tensor shape inference for `ConvTranspose2d` to work without a bias term (common with batch norm)

Reviewed By: rbgirshick

Differential Revision: D18076303

fbshipit-source-id: ccd95ad9475d33db4324edd115852aaa200e83d6

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2