### 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
icon->set_texture(gui_base->get_theme_icon(SNAME("Folder"), SNAME("EditorIcons")));
		} else {
			label->set_text(p_paths[i].get_file());
			icon->set_texture(gui_base->get_theme_icon(SNAME("File"), SNAME("EditorIcons")));
		}
		icon->set_stretch_mode(TextureRect::STRETCH_KEEP_CENTERED);
		icon->set_size(Size2(16, 16));
		hbox->add_child(icon);
		hbox->add_child(label);
		vbox->add_child(hbox);
	}
	if (p_paths.size() > num_rows) {
		Label *label = memnew(Label);
		if (has_file && has_folder) {
			label->set_text(vformat(TTR("%d more files or folders"), p_paths.size() - num_rows));
		} else if (has_folder) {
			label->set_text(vformat(TTR("%d more folders"), p_paths.size() - num_rows));
		} else {
			label->set_text(vformat(TTR("%d more files"), p_paths.size() - num_rows));
		}
		vbox->add_child(label);
	}
	p_from->set_drag_preview(vbox); 
	Dictionary drag_data;
	drag_data["type"] = has_folder ? "files_and_dirs" : "files";
	drag_data["files"] = p_paths;
	drag_data["from"] = p_from;
	return drag_data;
}
void EditorNode::add_tool_menu_item(const String &p_name, const Callable &p_callback) {