### 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 tab_closing_menu_option == FILE_QUIT || tab_closing_menu_option == RUN_PROJECT_MANAGER || tab_closing_menu_option == RELOAD_CURRENT_PROJECT;
}
void EditorNode::_scene_tab_closed(int p_tab, int p_option) {
	current_menu_option = p_option;
	tab_closing_idx = p_tab;
	Node *scene = editor_data.get_edited_scene_root(p_tab);
	if (!scene) {
		_discard_changes();
		return;
	}
	String scene_filename = scene->get_scene_file_path();
	String unsaved_message;
	if (EditorUndoRedoManager::get_singleton()->is_history_unsaved(editor_data.get_scene_history_id(p_tab))) {
		if (scene_filename.is_empty()) {
			unsaved_message = TTR("This scene was never saved.");
		} else {
			unsaved_message = vformat(TTR("Scene \"%s\" has unsaved changes."), scene_filename);