Error emitting !get_viewport()->gui_is_dragging() when using set_drag_preview from a sub-window

[Chaosus]

Godot version

Godot 4.0 / 7e5cd4b

System information

Windows 10

Issue description

When user try to drag something from subwindow - the error emitting at the set_drag_preview function. It's observed in a visual shader editor:

I think that's because gui.dragging boolean flag does not correctly transmit from sub-window to parent.

Steps to reproduce

^^

Minimal reproduction project

Too easy to reproduce in the visual shader editor.