### 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;
	}
	Error err = cf->load(addon_path);
	if (err != OK) {
		show_warning(vformat(TTR("Unable to enable addon plugin at: '%s' parsing of config failed."), addon_path));
		return;
	}
	String plugin_version;
	if (cf->has_section_key("plugin", "version")) {
		plugin_version = cf->get_value("plugin", "version");
	}
	if (!cf->has_section_key("plugin", "script")) {
		show_warning(vformat(TTR("Unable to find script field for addon plugin at: '%s'."), addon_path));
		return;
	}
	String script_path = cf->get_value("plugin", "script");
	Ref<Script> scr; 
	
	if (script_path.length() > 0) {
		script_path = addon_path.get_base_dir().path_join(script_path);
		scr = ResourceLoader::load(script_path, "Script", ResourceFormatLoader::CACHE_MODE_IGNORE);
		if (scr.is_null()) {
			show_warning(vformat(TTR("Unable to load addon script from path: '%s'."), script_path));
			return;
		}
		
		if (scr->get_instance_base_type() == StringName()) {
			if (_initializing_plugins) {
				
				pending_addons.push_back(p_addon);