[Caffe2] Fix merge logic bug (#89551)
Summary: `ExprGroup::getMergeCandidates()` had a logic bug. The vector being initialized had its arguments mis-ordered. This didn't trigger a build warning because the warning about implicit cast from an integral type to `bool` wasn't enabled.
Test Plan: `buck test fbsource//arvr/mode/win/vs2019/cuda11/opt fbsource//arvr/mode/hybrid_execution //arvr/libraries/neural_net_inference/TorchScript/...`
Differential Revision: D41488939
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89551
Approved by: https://github.com/davidberard98, https://github.com/jjsjann123
