Editor crashes on closing the additional inspector window which appears after the scene is playing with IAP Catalog open in Inspector.

Preconditions:
Requires Client ID from UDP dashboard or a project with UDP setup

Steps to repro:
1. Create a new Project
2. Window > Package Manager > Packages: Unity Registry
3. Search and Install UDP Package
5. Window > Unity Distribution Portal > IAP Catalog
6. Click on the Project window > Right-Click > Add tab > Inspector
7. Close the opened Inspector window
8. Play the scene

or

1. Create a new Project
2. Window > Package Manager > Packages: Unity Registry
3. Search and Install UDP Package
4. Window > Unity Distribution Portal > Settings
5. Use existing project ID or Create a new one
6. Link Client ID
7. Window > Unity Distribution Portal > IAP Catalog
8. Play and Stop a couple of times until an additional Inspector window pops up
9. Close the poped up Inspector window

Note: The Additional inspector window appears faster when using the Sample project under Package Manager UDP Package. Sometimes it takes a couple of tries until the Inspector window appears.

Actual Result:
Editor Crashes on closing Inspector window

Expected Result:
The inspector window closes seamlessly. Additionally, the empty inspector window shouldn't appear on the playing scene.

Reproducible on: 2021.2.0a3, 2021.1.0b4, 2021.1.0a6, 2020.2.2f1, 2019.1.0a1

Note: For 2019 open Window > Unity Distribution Portal > Settings
As the IAP catalog is not available.

Working on: 2018.4.29f1

First Affected Version: 2019.1.0a1

UDP Package Version: 2.1.4

Environment: Windows 10, Mac 10.15