Shortcut crashes when removed from SuperView and ColorScheme set to null

[tznind]

Describe the bug
Manifests in TGD when trying to delete a Shortcut

Error
Value cannot be null. (Parameter 'scheme')
   at System.ArgumentNullException.Throw(String paramName)
   at System.ArgumentNullException.ThrowIfNull(Object argument, String param
Name)
   at Terminal.Gui.ColorScheme..ctor(ColorScheme scheme)
   at Terminal.Gui.Shortcut.SetColors()
   at Terminal.Gui.Shortcut.set_ColorScheme(ColorScheme value)
   at TerminalGuiDesigner.SelectionManager.Clear(Boolean respectLock) in D:\
Repos\TerminalGuiDesigner\src\SelectionManager.cs:line 105
   at TerminalGuiDesigner.Operations.DeleteViewOperation.DoImpl() in D:\Rep
...

To Reproduce
Steps to reproduce the behavior:

1. Add a Shortcut to view area
2. Select it with rectangle selection
3. Press Delete
4. See error

Expected behavior
SetColors should handle this situation

Basically more null handling in SetColors please such that if base.ColorScheme is null it doesn't bomb

[tig]

@tznind when you file bugs, can you please set the label, project, and milestone so I don't have to do it?