Package manager window gets blank on changing Architecture settings in build settings.

Steps to repro:
1. Create a new project.
2. Window > Package Manager > Dock the Window.
3. File > Build Settings > Architecture > x86 to x86_64 OR x86_64 to x86 .

Actual Result:
Package manager window gets blank.

Expected Result:
Package manager window should not be blanked.

Workaround:
Close the Package Manager window and open again.

Reproducible in:
2019.3.0a12, 2019.3.0a11.

Working Fine in:
2019.3.0a10, 2019.2.0f1.

Environment:
Only on Windows.