### 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
for (int i = p_start; i < editor_data.get_edited_scene_count(); i++) {
		if (!editor_data.get_edited_scene_root(i)) {
			continue;
		}
		String scene_filename = editor_data.get_edited_scene_root(i)->get_scene_file_path();
		if (p_valid_filename && scene_filename.is_empty()) {
			continue;
		}
		bool unsaved = EditorUndoRedoManager::get_singleton()->is_history_unsaved(editor_data.get_scene_history_id(i));
		if (unsaved) {
			return i;
		} else {
			for (int j = 0; j < editor_data.get_editor_plugin_count(); j++) {
				if (!editor_data.get_editor_plugin(j)->get_unsaved_status(scene_filename).is_empty()) {
					return i;
				}
			}
		}
	}
	return -1;
}
void EditorNode::_exit_editor(int p_exit_code) {