Try to detect when the Visual isn't bound to a PresentationSource

[dstahl-axion]

Hi! I'm submitting this in the hopes you may be able to help me understand a problem we're facing and see if this is an appropriate solution.

Our application will sometimes (very rarely) crash inside line 40 in the element.PointToScreen(...) call. The stack trace looks like this:

Application Unhandled exception
(AppDomain.CurrentDomain.UnhandledException) in Application v1.0.0.0 EXCEPTION
OCCURRED:System.InvalidOperationException: This Visual is not connected to
a PresentationSource.
at System.Windows.Media.Visual.PointToScreen(Point point)
at
ToastNotifications.Position.ControlPositionProvider.GetPosition(Double
actualPopupWidth, Double actualPopupHeight)

I believe we see it when our application is up and a user is using Remote Desktop to connect. Looking through the code, I can see that this function would be invoked when the window is moved / resized and my hypothesis is that the remote desktop connection, particularly if the resolutions are different, could be causing some issue.

I don't fully understand the cause, but this ends up resulting in a hard crash of our software because this exception isn't caught. So I'm trying out this approach in a private build of this library but I wanted to open the PR here for discussion in case you can think of a better way to solve it.

Thanks for the library and I'm happy to answer any questions or help out in the solution.

Unfortunately, we cannot reliably reproduce this issue :( We just occasionally get a report from a user that it has crashed.