### 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
} else if (dock_slot[i]->get_tab_count() == 0) {
			dock_select->draw_rect(r, unused);
		} else {
			dock_select->draw_rect(r, used);
		}
		for (int j = 0; j < MIN(3, dock_slot[i]->get_tab_count()); j++) {
			int xofs = (r.size.width / 3) * j;
			Color c = used;
			if (i == dock_popup_selected_idx && (dock_slot[i]->get_current_tab() > 3 || dock_slot[i]->get_current_tab() == j)) {
				c = tab_selected;
			}
			dock_select->draw_rect(Rect2(2 + ofs.x + xofs, ofs.y, r.size.width / 3 - 1, 3), c);
		}
	}
}
void EditorNode::_save_editor_layout() {
	if (waiting_for_first_scan) {
		return; 
	}
	Ref<ConfigFile> config;
	config.instantiate();
	
	config->load(EditorPaths::get_singleton()->get_project_settings_dir().path_join("editor_layout.cfg"));
	_save_docks_to_config(config, "docks");
	_save_open_scenes_to_config(config);
	_save_central_editor_layout_to_config(config);
	editor_data.get_plugin_window_layout(config);
	config->save(EditorPaths::get_singleton()->get_project_settings_dir().path_join("editor_layout.cfg"));
}
void EditorNode::_save_docks_to_config(Ref<ConfigFile> p_layout, const String &p_section) {