[USER32][WIN32SS] An owned window should be hidden when its owner is minimized

https://github.com/reactos/reactos/pull/668
I'm working on "Show the Desktop" feature. I found a fatal bug on it.

https://docs.microsoft.com/en-us/windows/desktop/winmsg/window-features#owned-windows

An owned window is hidden when its owner is minimized.

I made two test programs to investigate this problem. This is it: https://github.com/katahiromz/wintest

1. Execute target.exe.
2. A window with a modal dialog will be started.
3. Read the title bar's window handle value.
4. Execute minimize.exe with the window handle value.

This test should minimize the target.exe windows but ReactOS fails. The modal dialog remains.
Screenshots: ros-dont-minimize.png, win10-wintest.png