fix: use optional chaining when checking router type (#13218)

* fix: use optional chaining when checking router type

* no need for changeset, nothing was released yet

* Revert "no need for changeset, nothing was released yet"

This reverts commit cff720b.

Author: Rich-Harris

.changeset/strange-wolves-draw.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-static': patch
+---
+
+fix: use optional chaining when checking router type

packages/adapter-static/index.js

@@ -7,7 +7,7 @@ export default function (options) {
 		name: '@sveltejs/adapter-static',
 
 		async adapt(builder) {
-			if (!options?.fallback && builder.config.kit.router.type !== 'hash') {
+			if (!options?.fallback && builder.config.kit.router?.type !== 'hash') {
 				const dynamic_routes = builder.routes.filter((route) => route.prerender !== true);
 				if (dynamic_routes.length > 0 && options?.strict !== false) {
 					const prefix = path.relative('.', builder.config.kit.files.routes);