### 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 (gui_base) {
		if (gui_base->has_theme_icon(p_class, SNAME("EditorIcons"))) {
			return gui_base->get_theme_icon(p_class, SNAME("EditorIcons"));
		}
		if (p_fallback.length() && gui_base->has_theme_icon(p_fallback, SNAME("EditorIcons"))) {
			return gui_base->get_theme_icon(p_fallback, SNAME("EditorIcons"));
		}
	}
	return nullptr;
}
Ref<Texture2D> EditorNode::get_object_icon(const Object *p_object, const String &p_fallback) {
	ERR_FAIL_NULL_V_MSG(p_object, nullptr, "Object cannot be null.");
	Ref<Script> scr = p_object->get_script();
	if (scr.is_null() && p_object->is_class("Script")) {
		scr = p_object;
	}
	return _get_class_or_script_icon(p_object->get_class(), scr, p_fallback);
}
Ref<Texture2D> EditorNode::get_class_icon(const String &p_class, const String &p_fallback) {
	ERR_FAIL_COND_V_MSG(p_class.is_empty(), nullptr, "Class name cannot be empty.");
	Ref<Script> scr;
	if (ScriptServer::is_global_class(p_class)) {
		scr = EditorNode::get_editor_data().script_class_load_script(p_class);
	}
	return _get_class_or_script_icon(p_class, scr, p_fallback);
}
bool EditorNode::is_object_of_custom_type(const Object *p_object, const StringName &p_class) {