Handle empty qconfig for functional Modules (#24803)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24803
ghstack-source-id: 89003797
Test Plan: Test implemented in D16879132/
Differential Revision: D16879133
fbshipit-source-id: 230f5204cfbd149fea1c0985578a2572a0e0f2a8
