[caffe2][debuggability] add length checks to MergeMultiScalarFeatureTensors (#36248)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36248
Add basic index/length checks to MergeMultiScalarFeatureTensors to avoid segfaults.
But I don't really understand this op: what would cause this mismatch (see test plan) -- would iike to add it to the assertion description.
Reviewed By: houseroad
Differential Revision: D20912048
fbshipit-source-id: 29ef8c4bd261a48d64cbef6aa4f0306d7f058e71
