fix: page loading message does not persist

src/components/PageProgress.tsx

@@ -14,6 +14,10 @@ export function PageProgress(props: Props) {
   const $pageProgressMessage = useStore(pageProgressMessage);
 
   useEffect(() => {
+    if ($pageProgressMessage === undefined) {
+      return;
+    }
+
     setMessage($pageProgressMessage);
   }, [$pageProgressMessage]);
 

src/stores/page.ts

@@ -1,4 +1,4 @@
 import { atom } from 'nanostores';
 
-export const pageProgressMessage = atom('');
+export const pageProgressMessage = atom<string | undefined>(undefined);
 export const sponsorHidden = atom(false);