### 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
switch (current_menu_option) {
		case FILE_NEW_INHERITED_SCENE: {
			Node *scene = editor_data.get_edited_scene_root();
			
			if (!scene) {
				_menu_option_confirm(FILE_CLOSE, true);
			}
			load_scene(p_file, false, true);
		} break;
		case FILE_OPEN_SCENE: {
			load_scene(p_file);
		} break;
		case SETTINGS_PICK_MAIN_SCENE: {
			ProjectSettings::get_singleton()->set("application/run/main_scene", p_file);
			ProjectSettings::get_singleton()->save();
			
			project_run_bar->play_main_scene((bool)pick_main_scene->get_meta("from_native", false));
		} break;
		case FILE_CLOSE:
		case SCENE_TAB_CLOSE:
		case FILE_SAVE_SCENE:
		case FILE_SAVE_AS_SCENE: {
			int scene_idx = (current_menu_option == FILE_SAVE_SCENE || current_menu_option == FILE_SAVE_AS_SCENE) ? -1 : tab_closing_idx;
			if (file->get_file_mode() == EditorFileDialog::FILE_MODE_SAVE_FILE) {
				bool same_open_scene = false;