### 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
window->set_theme(theme);
			}
			OS::get_singleton()->set_low_processor_usage_mode_sleep_usec(int(EDITOR_GET("interface/editor/low_processor_mode_sleep_usec")));
			get_tree()->get_root()->set_as_audio_listener_3d(false);
			get_tree()->get_root()->set_as_audio_listener_2d(false);
			get_tree()->get_root()->set_snap_2d_transforms_to_pixel(false);
			get_tree()->get_root()->set_snap_2d_vertices_to_pixel(false);
			get_tree()->set_auto_accept_quit(false);
#ifdef ANDROID_ENABLED
			get_tree()->set_quit_on_go_back(false);
#endif
			get_tree()->get_root()->connect("files_dropped", callable_mp(this, &EditorNode::_dropped_files));
			command_palette->register_shortcuts_as_command();
			MessageQueue::get_singleton()->push_callable(callable_mp(this, &EditorNode::_begin_first_scan));
			
		} break;
		case NOTIFICATION_EXIT_TREE: {
			if (progress_dialog) {
				progress_dialog->queue_free();
			}
			if (load_error_dialog) {
				load_error_dialog->queue_free();
			}
			if (execute_output_dialog) {
				execute_output_dialog->queue_free();
			}
			if (warning) {
				warning->queue_free();
			}
			if (accept) {