Exiting RAPPS after changing theme makes Win32k assert and hang system

Originally reported by: https://twitter.com/da_snowbird/status/1320818547333935105

I was able to reproduce it in a simpler way, here are steps:

1. Make sure you have classic theme set
2. Start RAPPS and wait until its main window is ready
3. Open desktop properties
4. Change theme to Lautus and apply it with "OK" button
5. Switch to RAPPS and close it with "X" window button

Expected behavior:

• RAPPS closes silently without problems

Observed behavior:

• 0.4.14-dev-1307-g1437433:
  • Normal mode: ATL assertion window appears, system hangs
  • Debug mode: ATL assertion window appears, breaks into debugger, but after cont it immediately disappears, and system is still working after (minor: BSOD on shutdown attempt)
• 0.4.15-dev-1201-gb2cf5a4 (latest):
  • Normal mode: ATL assertion window appears, then immediately disappears, then system hangs
  • Debug mode: ATL assertion window appears, then immediately disappears, then breaks into debugger, and system is still working fine after cont command (no BSOD on shutdown)

By doing git bisect I was able to find a group of guilty commits by learn_more, I think they are just unhiders:

There are only 'skip'ped commits left to test.

The first bad commit could be any of:

1437433039a525004ad0267a7361e9d788e745cc

4439b538007bdf5dd2f4b3e52e079363f73b946d

bcd301d136f7c05d5052a9ded51e2123f3c32078

We cannot bisect more!

Debug logs attached for guilty and latest: 0.4.14-dev-1307-g1437433.log 0.4.15-dev-1201-gb2cf5a4.log

Additional debug log with forced retry on dbgrpt.cpp line 182 using return IDRETRY; and Appcrash log produced by it attached - assert-retry-0.4.15-dev-1201-gb2cf5a4.log Appcrash_2020-10-27_14-01-52.txt