### Godot version

v4.2.dev.custom_build [0c2144da9]

### System information

Debian Linux X11 Xfce

### Issue description

Prerequisite: Be in Single Window Mode in the Editor
The Filesystem Dock is unusable when it is floating, which is not expected.
It appears garbled in the top-left corner:
![image](https://github.com/godotengine/godot/assets/6299227/109f7922-97de-44c3-814a-ca7f970e0602)

The following errors are shown:
```
  editor/window_wrapper.cpp:220 - Condition "!is_window_available()" is true.
  editor/window_wrapper.cpp:202 - Condition "!get_window_enabled()" is true. Returning: Rect2i()
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
  editor/window_wrapper.cpp:207 - Condition "!get_window_enabled()" is true. Returning: -1
```

bisecting lead to #62378
possibly related to #44439

### Steps to reproduce

1. Start a project in the Editor
2. Switch to Single Window Mode in the Editor and reload (if necessary)
3. Make the Filesystem Dock floating

### Minimal reproduction project

Editor issue
Control *dock = nullptr;
	for (int i = 0; i < DOCK_SLOT_MAX; i++) {
		if (p_control->get_parent() == dock_slot[i]) {
			dock = dock_slot[i];
			break;
		}
	}
	ERR_FAIL_COND_MSG(!dock, "Control was not in dock.");
	dock->remove_child(p_control);
	_update_dock_slots_visibility();
}
Variant EditorNode::drag_resource(const Ref<Resource> &p_res, Control *p_from) {
	Control *drag_control = memnew(Control);
	TextureRect *drag_preview = memnew(TextureRect);
	Label *label = memnew(Label);
	Ref<Texture2D> preview;
	{
		
		Ref<ImageTexture> texture = gui_base->get_theme_icon(SNAME("FileBigThumb"), SNAME("EditorIcons"));
		Ref<Image> img = texture->get_image();
		img = img->duplicate();
		img->resize(48, 48); 
		preview = ImageTexture::create_from_image(img);
	}
	drag_preview->set_texture(preview);
	drag_control->add_child(drag_preview);
	if (p_res->get_path().is_resource_file()) {
		label->set_text(p_res->get_path().get_file());
	} else if (!p_res->get_name().is_empty()) {