Fix installer dialogs that remain open after confirmation

[bubblegump30]

 * @param onStateSetter Called with the modal's state setter once the component
 *   mounts — lets the caller swap content without touching pluginSelf.
 */
async PromptInstallation(type: InstallType, data: any, onStateSetter: (setter: (el: React.ReactElement) => void) => void): Promise<ShowModalResult> {
async PromptInstallation(type: InstallType, data: any, onStateSetter: (setter: (el: React.ReactElement) => void) => void): Promise<ShowModalResult | null> {
	const itemName = (type === InstallType.Plugin ? data?.pluginJson?.common_name : data?.name) ?? locale.strUnknown;

	return new Promise((resolve) => {
					onOK={() => resolve(modal)}
					bHideCloseIcon={true}
					closeModal={() => {}}
					onCancel={() => modal?.Close()}
					onCancel={() => {
						modal?.Close();
						resolve(null);
					}}
				/>,
			);


	function ShowMessageBox(message: React.ReactNode, title: React.ReactNode, props?: ConfirmModalProps) {
		return new Promise((resolve) => {
			let standaloneModal: ShowModalResult | undefined;
			const handle = (result: boolean, cb?: () => void) => {
				cb?.();
				// A message with no custom action is terminal. The installer owns
				// this modal, so Steam cannot dismiss it automatically.
				if (!cb) {
					(updateInstallerState ? modal : standaloneModal)?.Close();
				}
				resolve(result);
			};

			if (updateInstallerState) {
				updateInstallerState(element);
			} else {
				showModal(element, pluginSelf.mainWindow, {
				standaloneModal = showModal(element, pluginSelf.mainWindow, {
					bNeverPopOut: true,
					popupWidth: 500,
					popupHeight: 275,
		modal = await this.PromptInstallation(type, data, (setter) => {
			updateInstallerState = setter;
		});
		if (!modal) return;

		// updateInstallerState is guaranteed set here — the Renderer useEffect
		// fires before the user can click OK.