Update client.js

Author: GauBen

packages/kit/src/runtime/client/client.js

@@ -2552,7 +2552,7 @@ function _start_router() {
 			if (history_index === current_history_index) return;
 
 			const scroll = scroll_positions[history_index];
-			const state = unstringify(event.state[STATES_KEY], app.hooks.transport) ?? {};
+			const state = event.state[STATES_KEY] ? unstringify(event.state[STATES_KEY], app.hooks.transport) : {};
 			const url = new URL(event.state[PAGE_URL_KEY] ?? location.href);
 			const navigation_index = event.state[NAVIGATION_INDEX];
 			const is_hash_change = current.url ? strip_hash(location) === strip_hash(current.url) : false;