### 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
scene_tabs_context_menu->add_shortcut(ED_GET_SHORTCUT("editor/reopen_closed_scene"), FILE_OPEN_PREV);
				scene_tabs_context_menu->set_item_text(scene_tabs_context_menu->get_item_index(FILE_OPEN_PREV), TTR("Undo Close Tab"));
				if (previous_scenes.is_empty()) {
					scene_tabs_context_menu->set_item_disabled(scene_tabs_context_menu->get_item_index(FILE_OPEN_PREV), true);
				}
				scene_tabs_context_menu->add_item(TTR("Close Other Tabs"), FILE_CLOSE_OTHERS);
				scene_tabs_context_menu->add_item(TTR("Close Tabs to the Right"), FILE_CLOSE_RIGHT);
				scene_tabs_context_menu->add_item(TTR("Close All Tabs"), FILE_CLOSE_ALL);
			}
			scene_tabs_context_menu->set_position(scene_tabs->get_screen_position() + mb->get_position());
			scene_tabs_context_menu->reset_size();
			scene_tabs_context_menu->popup();
		}
	}
}
void EditorNode::_reposition_active_tab(int idx_to) {
	editor_data.move_edited_scene_to_index(idx_to);
	_update_scene_tabs();
}
void EditorNode::_thumbnail_done(const String &p_path, const Ref<Texture2D> &p_preview, const Ref<Texture2D> &p_small_preview, const Variant &p_udata) {
	int p_tab = p_udata.operator signed int();
	if (p_preview.is_valid()) {
		Rect2 rect = scene_tabs->get_tab_rect(p_tab);
		rect.position += scene_tabs->get_global_position();
		tab_preview->set_texture(p_preview);
		tab_preview_panel->set_position(rect.position + Vector2(0, rect.size.height));
		tab_preview_panel->show();
	}
}
void EditorNode::_scene_tab_changed(int p_tab) {