PCem does not seem to close when main window closes on Windows.

[michael-manley]

Describe the bug
When I was running PCem latest to verify some build changes, I noticed on when I was deleting the folder it was not allowing
it to be deleted. This is when I noticed that it did not close the whole program after close. The main window is gone but it still
is running in the background.

To Reproduce
Steps to reproduce the behavior:

1. Open PCem
2. Close PCem

Expected behavior
PCem Does not continue to run in background

Screenshots

Host machine

• OS: Windows 10 Enterprise
• Emulator version: PCem vNext 0ec21db