### 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
Node *old_edited_scene_root = get_editor_data().get_edited_scene_root();
	if (old_edited_scene_root) {
		if (old_edited_scene_root->get_parent() == scene_root) {
			scene_root->remove_child(old_edited_scene_root);
		}
		old_edited_scene_root->disconnect(SNAME("replacing_by"), callable_mp(this, &EditorNode::set_edited_scene));
	}
	get_editor_data().set_edited_scene_root(p_scene);
	if (Object::cast_to<Popup>(p_scene)) {
		Object::cast_to<Popup>(p_scene)->show();
	}
	SceneTreeDock::get_singleton()->set_edited_scene(p_scene);
	if (get_tree()) {
		get_tree()->set_edited_scene_root(p_scene);
	}
	if (p_scene) {
		if (p_scene->get_parent() != scene_root) {
			scene_root->add_child(p_scene, true);
		}
		p_scene->connect(SNAME("replacing_by"), callable_mp(this, &EditorNode::set_edited_scene));
	}
}
int EditorNode::_get_current_main_editor() {