### 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
if (p_resource->get_path().is_resource_file()) {
			file->set_current_file(p_resource->get_path().get_file());
		} else {
			if (extensions.size()) {
				String resource_name_snake_case = p_resource->get_class().to_snake_case();
				file->set_current_file("new_" + resource_name_snake_case + "." + preferred.front()->get().to_lower());
			} else {
				file->set_current_file(String());
			}
		}
	} else if (!p_resource->get_path().is_empty()) {
		file->set_current_path(p_resource->get_path());
		if (extensions.size()) {
			String ext = p_resource->get_path().get_extension().to_lower();
			if (extensions.find(ext) == nullptr) {
				file->set_current_path(p_resource->get_path().replacen("." + ext, "." + extensions.front()->get()));
			}
		}
	} else if (preferred.size()) {
		String existing;
		if (extensions.size()) {
			String resource_name_snake_case = p_resource->get_class().to_snake_case();
			existing = "new_" + resource_name_snake_case + "." + preferred.front()->get().to_lower();
		}
		file->set_current_path(existing);
	}
	file->set_title(TTR("Save Resource As..."));
	file->popup_file_dialog();
}
void EditorNode::_menu_option(int p_option) {