Only import PIL when needed (#23023)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/22389
In most cases we only import `PIL` methods when we need them, but we missed a spot.
cc lanpa natalialunova sanekmelnikov
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23023
Reviewed By: sanekmelnikov
Differential Revision: D16373492
Pulled By: orionr
fbshipit-source-id: b08bf8a9b5a861390eadf62eda21ac055777180f
