### 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
DEV_ASSERT(Thread::get_caller_id() == Thread::get_main_id());
	singleton->load_errors->add_image(singleton->gui_base->get_theme_icon(SNAME("Warning"), SNAME("EditorIcons")));
	singleton->load_errors->add_text(p_warning + "\n");
	EditorInterface::get_singleton()->popup_dialog_centered_ratio(singleton->load_error_dialog, 0.5);
}
bool EditorNode::_find_scene_in_use(Node *p_node, const String &p_path) const {
	if (p_node->get_scene_file_path() == p_path) {
		return true;
	}
	for (int i = 0; i < p_node->get_child_count(); i++) {
		if (_find_scene_in_use(p_node->get_child(i), p_path)) {
			return true;
		}
	}
	return false;
}
bool EditorNode::is_scene_in_use(const String &p_path) {
	Node *es = get_edited_scene();
	if (es) {
		return _find_scene_in_use(es, p_path);
	}
	return false;
}
OS::ProcessID EditorNode::has_child_process(OS::ProcessID p_pid) const {
	return project_run_bar->has_child_process(p_pid);
}
void EditorNode::stop_child_process(OS::ProcessID p_pid) {