### 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
if (!bool(EDITOR_GET("interface/scene_tabs/restore_scenes_on_load"))) {
		return false;
	}
	Ref<ConfigFile> config;
	config.instantiate();
	Error err = config->load(EditorPaths::get_singleton()->get_project_settings_dir().path_join("editor_layout.cfg"));
	if (err != OK) {
		return false;
	}
	if (!config->has_section(EDITOR_NODE_CONFIG_SECTION) || !config->has_section_key(EDITOR_NODE_CONFIG_SECTION, "open_scenes")) {
		return false;
	}
	Array scenes = config->get_value(EDITOR_NODE_CONFIG_SECTION, "open_scenes");
	return !scenes.is_empty();
}
bool EditorNode::ensure_main_scene(bool p_from_native) {