[lint] Fix uninitialized variable lint error in `Module.cpp` (#58499)
Summary:
This PR fixes two uninitialized variable lint warnings in `Module.cpp` by initializing them to `nullptr`s.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58499
Reviewed By: driazati, samestep
Differential Revision: D28519192
Pulled By: 1ntEgr8
fbshipit-source-id: 293cd4b296eea70b72adf02cd73f354063b124c6
