### 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
exiting = true;
	resource_preview->stop(); 
	_save_editor_layout();
	
	dim_editor(true);
	get_tree()->quit(p_exit_code);
}
void EditorNode::_discard_changes(const String &p_str) {
	switch (current_menu_option) {
		case FILE_CLOSE:
		case SCENE_TAB_CLOSE: {
			Node *scene = editor_data.get_edited_scene_root(tab_closing_idx);
			if (scene != nullptr) {
				String scene_filename = scene->get_scene_file_path();
				if (!scene_filename.is_empty()) {
					previous_scenes.push_back(scene_filename);
				}
			}
			
			if (!_is_closing_editor()) {
				_remove_scene(tab_closing_idx);
				_update_scene_tabs();