Xaml sample closes DocumentDock when last document is closed

[MihaMarkic]

Try running Xaml sample and close both documents. DocumentDock disappears from DockControl.
Tested on master branch. Looks like a bug.

[MihaMarkic]

Looks like the culprit is in FactoryBase.Dockable.cs file, mehtod CloseDockable where calling RemoveDockable(dockable, true); - collapse is true which means that DocumentDock would collapse when it has no documents.

[MihaMarkic]

Applying IsCollapsable="False" on DocumentDock control fixes it.