torch.cuda.memory_allocated to return `{}` if not initialized (#51179)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/49952
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51179
Reviewed By: ngimel
Differential Revision: D26094932
Pulled By: malfet
fbshipit-source-id: 0ec28ef9b0604245753d3f2b0e3536286700668d
