NullReferenceException in ActionMessage when EnableGuardDuringInvocation is enabled without guard (WPF, not MAUI)

[MartinBuehlmann]

The invocation of an ActionMessage results in a NullReferenceException when used in a WPF application if EnableGuardDuringInvocation is set to true and no guard exists.

It looks like someone tried to optimize the null check by using the ? syntax, but in fact the _context was checked against null instead of the Func CanExecute.

See ActionMessage.cs
if (EnforceGuardsDuringInvocation && _!context?.CanExecute())
{
return;
}

I laready prepared a pull request:
#1021

[vb2ae]

@MartinBuehlmann thank you