### 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
const Size2 add_button_size = Size2(0, scene_tabs->get_size().y);
	if (scene_tabs->get_offset_buttons_visible()) {
		
		if (scene_tab_add->get_parent() == scene_tabs) {
			scene_tabs->remove_child(scene_tab_add);
			scene_tab_add_ph->add_child(scene_tab_add);
			scene_tab_add->set_rect(Rect2(Point2(), add_button_size));
		}
	} else {
		
		if (scene_tab_add->get_parent() == scene_tab_add_ph) {
			scene_tab_add_ph->remove_child(scene_tab_add);
			scene_tabs->add_child(scene_tab_add);
		}
		if (scene_tabs->get_tab_count() == 0) {
			scene_tab_add->set_rect(Rect2(Point2(), add_button_size));
			return;
		}
		Rect2 last_tab = scene_tabs->get_tab_rect(scene_tabs->get_tab_count() - 1);
		int hsep = scene_tabs->get_theme_constant(SNAME("h_separation"));
		if (scene_tabs->is_layout_rtl()) {
			scene_tab_add->set_rect(Rect2(Point2(last_tab.position.x - scene_tab_add->get_size().x - hsep, last_tab.position.y), add_button_size));
		} else {
			scene_tab_add->set_rect(Rect2(Point2(last_tab.position.x + last_tab.size.width + hsep, last_tab.position.y), add_button_size));
		}
	}
	
	scene_tabs->connect("tab_changed", callable_mp(this, &EditorNode::_scene_tab_changed));
}
void EditorNode::_version_control_menu_option(int p_idx) {