Retrieves a gdk.Cursor pointer for the cursor currently set on the
specified gdk.Window, or NULL. If the return value is NULL then
there is no custom cursor set on the specified window, and it is
using the cursor for its parent window.
a gdk.Cursor, or NULL. The
returned object is owned by the gdk.Window and should not be
unreferenced directly. Use Window.setCursor to unset the
cursor of the window