fix tuple indexing bug (#21521)
Summary:
lower tuples pass didn't check bounds for tuple index
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21521
Differential Revision: D15716813
Pulled By: eellison
fbshipit-source-id: 8eead98c2c63118e7d24a8c8bf6184b02afb7dcd
