[FZ Editor] Crash when creating a new layout

[enricogior]

The new FZ Editor 646d61b has a rare crashing bug when creating a new layout.
Repro steps:

• open the editor and click on "+ Create new layout"
• click on "Create" (it doesn't matter if you choose Grid or Canvas)

Result: the editor crashes.
If the problem presents itself, it reproduces 100% of the times. Restarting PowerToys or Windows doesn't make any change. Re-installing PT or running a local build doesn't make any difference.
It happens on both .NET Core 3.1.10 and 3.1.11.

Description: The process was terminated due to an unhandled exception.
Exception Info: System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values. (Parameter 'index')
   at System.Windows.Media.VisualCollection.get_Item(Int32 index)
   at System.Windows.Media.Visual.InternalGet2DOr3DVisualChild(Int32 index)

Full event log call stack attached.

event log.txt

[crutkas]

dotnet/roslyn#17232 has a very close call stack

[crutkas]

none of my computers can repro

thoughts:

1. move Hide() to either top or bottom of method. The call is nested inside an area that is messing with data contexts.
2. Wrap the Hide in a dispatcher.invoke
3. what happens if we try/catch the hide? The call stack looks like it is getting into some type of recursive tree and fails.

[enricogior]

1. already tried
2. already tried
3. I tried to catch and call again Hide() inside the catch... it worked, no idea why, but it doesn't crash a second time.