### 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 export_as_menu;
}
void EditorNode::_global_menu_scene(const Variant &p_tag) {
	int idx = (int)p_tag;
	scene_tabs->set_current_tab(idx);
}
void EditorNode::_global_menu_new_window(const Variant &p_tag) {
	if (OS::get_singleton()->get_main_loop()) {
		List<String> args;
		args.push_back("-p");
		OS::get_singleton()->create_instance(args);
	}
}
void EditorNode::_dropped_files(const Vector<String> &p_files) {
	String to_path = ProjectSettings::get_singleton()->globalize_path(FileSystemDock::get_singleton()->get_current_directory());
	_add_dropped_files_recursive(p_files, to_path);
	EditorFileSystem::get_singleton()->scan_changes();
}
void EditorNode::_add_dropped_files_recursive(const Vector<String> &p_files, String to_path) {