The editor crashes because of closing the editor while exporting a package.

It crashes because we try to access a reference to AsyncReadManager that was already set to null during an earlier call to Application.Shutdown() from TickPackageImport().
Investigation notes and call stacks here:
https://docs.google.com/document/d/1MU7tM7J-D4glUC83AYwpi2aQmUwHomUVYDElhTZh7g8/edit

Steps to reproduce:
1) Create a new project.
2) Add a large number of assets to your project, e.g. by importing a big package from the asset store.
4) Right Click in Project > Export package. Export all assets.
5) Wait for the progress window to display the text "Compressing Package...".
6) Right Click Unity from taskbar > Close the Unity Editor Window.

Actual Result: Editor crashes after the package is exported

Expected result: Editor should not crash on closing the window

Occurring on: 2022.2.0a6, 2021.2.0a1, 2021.1.0b2, 2020.2.2f1, 2020.1.10f1, 2019.4.12f1

Environment: Only on Windows