### 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
quick_open->set_title(TTR("Quick Open..."));
		} break;
		case FILE_QUICK_OPEN_SCENE: {
			quick_open->popup_dialog("PackedScene", true);
			quick_open->set_title(TTR("Quick Open Scene..."));
		} break;
		case FILE_QUICK_OPEN_SCRIPT: {
			quick_open->popup_dialog("Script", true);
			quick_open->set_title(TTR("Quick Open Script..."));
		} break;
		case FILE_OPEN_PREV: {
			if (previous_scenes.is_empty()) {
				break;
			}
			opening_prev = true;
			open_request(previous_scenes.back()->get());
			previous_scenes.pop_back();
		} break;
		case FILE_CLOSE_OTHERS: {
			tab_closing_menu_option = -1;
			for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
				if (i == editor_data.get_edited_scene()) {
					continue;
				}
				tabs_to_close.push_back(editor_data.get_scene_path(i));
			}
			_proceed_closing_scene_tabs();
		} break;
		case FILE_CLOSE_RIGHT: {
			tab_closing_menu_option = -1;