[DataLoader] Remove redundant len >= 0 (#57951)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57951
As pmeier suggested in another PR, just remove all redundant check for prior DataPipe.
Test Plan: Imported from OSS
Reviewed By: mruberry
Differential Revision: D28325414
Pulled By: ejguan
fbshipit-source-id: 17497745fef1647c24a25f4ca08082dd4df6f4a7
