### 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
String addon_path = p_addon;
	if (!addon_path.begins_with("res:")) {
		addon_path = "res:addons/" + addon_path + "/plugin.cfg";
	}
	ERR_FAIL_COND(p_enabled && addon_name_to_plugin.has(addon_path));
	ERR_FAIL_COND(!p_enabled && !addon_name_to_plugin.has(addon_path));
	if (!p_enabled) {
		EditorPlugin *addon = addon_name_to_plugin[addon_path];
		remove_editor_plugin(addon, p_config_changed);
		memdelete(addon);
		addon_name_to_plugin.erase(addon_path);
		_update_addon_config();
		return;
	}
	Ref<ConfigFile> cf;
	cf.instantiate();
	if (!DirAccess::exists(addon_path.get_base_dir())) {
		_remove_plugin_from_enabled(addon_path);
		WARN_PRINT("Addon '" + addon_path + "' failed to load. No directory found. Removing from enabled plugins.");