### 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
return true;
				}
			}
		}
	} else {
		
		if (FileAccess::exists(path + ".import")) {
			return true;
		}
	}
	return false;
}
void EditorNode::request_instantiate_scene(const String &p_path) {
	SceneTreeDock::get_singleton()->instantiate(p_path);
}
void EditorNode::request_instantiate_scenes(const Vector<String> &p_files) {
	SceneTreeDock::get_singleton()->instantiate_scenes(p_files);
}
void EditorNode::_inherit_request(String p_file) {
	current_menu_option = FILE_NEW_INHERITED_SCENE;
	_dialog_action(p_file);
}
void EditorNode::_instantiate_request(const Vector<String> &p_files) {
	request_instantiate_scenes(p_files);
}
void EditorNode::_close_messages() {
	old_split_ofs = center_split->get_split_offset();
	center_split->set_split_offset(0);
}
void EditorNode::_show_messages() {