[TensorExpr] Eliminate Cond statements when each branch is a different kind of empty (#39754)
Summary:
Fix another simplification edge case, a Cond statement when one branch is nullptr and the other is a zero stmt block. This happens mostly with an if with no else branch where all statements inside the if are removed (eg via inlining or simplification). Common case is SplitWithMask -> ComputeInline.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39754
Differential Revision: D21962987
Pulled By: nickgg
fbshipit-source-id: 2461415466fbbab88d2329061f90fcfdfa85e243
