Handle empty qconfig for functional Modules (#25215)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25215
ghstack-source-id: 89044252
Test Plan: Test implemented in D16879132/
Differential Revision: D17064670
fbshipit-source-id: 08d3d566aa123bedf318ab5a8bc9b71457930ff2
