### 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
unsaved_scenes += "\n            " + editor_data.get_edited_scene_root(i)->get_scene_file_path();
						i = _next_unsaved_scene(true, ++i);
					}
					if (p_option == RELOAD_CURRENT_PROJECT) {
						save_confirmation->set_ok_button_text(TTR("Save & Reload"));
						save_confirmation->set_text(TTR("Save changes to the following scene(s) before reloading?") + unsaved_scenes);
					} else {
						save_confirmation->set_ok_button_text(TTR("Save & Quit"));
						save_confirmation->set_text((p_option == FILE_QUIT ? TTR("Save changes to the following scene(s) before quitting?") : TTR("Save changes to the following scene(s) before opening Project Manager?")) + unsaved_scenes);
					}
					save_confirmation->reset_size();
					save_confirmation->popup_centered();
				}
				DisplayServer::get_singleton()->window_request_attention();
				break;
			}
			_save_external_resources();
			_discard_changes();
		} break;
		case SETTINGS_UPDATE_CONTINUOUSLY: {
			EditorSettings::get_singleton()->set("interface/editor/update_continuously", true);
			_update_update_spinner();
			show_accept(TTR("This option is deprecated. Situations where refresh must be forced are now considered a bug. Please report."), TTR("OK"));
		} break;
		case SETTINGS_UPDATE_WHEN_CHANGED: {
			EditorSettings::get_singleton()->set("interface/editor/update_continuously", false);
			_update_update_spinner();
		} break;
		case SETTINGS_UPDATE_SPINNER_HIDE: {
			EditorSettings::get_singleton()->set("interface/editor/show_update_spinner", false);