metro window keeps glow on top of owned window on restored

[MajedDH]

Describe the bug
When you show a MetroWindow and show another one with the first one as an owner and you minimize the main one, it's glow is still visible above the owned one.

To Reproduce
Steps to reproduce the behavior:

1. Create a MetroWindow and show it.
2. Inside it (on click or load) create another metro window and set it's owner to the first one.
3. now maximize the main window
4. Click on the child window to activate it
5. click on the minimize button of the main window
6. you can see that only the glow is still visible above the child window
7. If you switch to the main window and then switch to the child window, then the expected behavior is done.
   Expected behavior
   the glow should be behind the child window.
   Screenshots

the bug:

the expected bihavior:

Environment(please complete the following information):

• MahApps.Metro version 1.6.4
• OS: Win 7
• Visual Studio 2017 15.3.2
• .NET Framework 4.6

[batzen]

This issue will be fixed in ControlzEx as MahApps.Metro will depend on the GlowWindow etc. from there in the future.
If it's a small fix i might port it back to the current version of MahApps.

[batzen]

Fixed in the ControlzEx version of the behavior now.