### 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
EditorFileSystemDirectory *efsd = EditorFileSystem::get_singleton()->get_filesystem_path(p_path.get_base_dir());
	if (efsd) {
		String file = p_path.get_file();
		for (int i = 0; i < efsd->get_file_count(); i++) {
			if (efsd->get_file(i) == file) {
				String type = efsd->get_file_type(i);
				if (singleton->icon_type_cache.has(type)) {
					return singleton->icon_type_cache[type];
				} else {
					return singleton->icon_type_cache["Object"];
				}
			}
		}
	}
	return singleton->icon_type_cache["Object"];
}
void EditorNode::_build_icon_type_cache() {