[quant][graphmode][fx][fix] Support None qconfig in convert (#44524)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44524
None qconfig is not handled previously
closes: https://github.com/pytorch/pytorch/issues/44438
Test Plan: Imported from OSS
Reviewed By: vkuzo
Differential Revision: D23640269
fbshipit-source-id: 8bfa88c8c78d4530338d9d7fa9669876c386d91f
