Handle run.py model_analyzer is none (#1297)
Summary:
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1297
When model_analyzer is None, it will get an error when referenced without assignment. By default, set model_analyzer to None, and use this to check if analyzer is enabled.
Test Plan: CI
Reviewed By: xuzhao9, yuguo68, FindHao
Differential Revision: D41202708
Pulled By: aaronenyeshi
fbshipit-source-id: 352546ed4dafd0363ae5835e60c84859c2a62a24
