Fix error with desktop-icons-extension, dragging and dropping on workspace thumbnail allows the desktop window to be dragged and dropped.
If a window is on all workspaces, there is no point dragging it to a different workspace, disable drag and drop for these windows to a different workspace. Otherwise Meta forcibly removes the window.stick() on these type of windows.
If a window is of type Meta.WindowType.DESKTOP, do not display on the workspace thumbnail. As a consequence, this type of window cannot be dragged and dropped to a different workspace.
Fix for #456
Edited by Sundeep Mediratta