Add the site meta to the 404 page when looking for posts.

src/routes/posts.tsx

@@ -15,11 +15,14 @@ app.get('/:slug', async (c) => {
   const postFile = files.find(f => f === fileName);
   if (!postFile) {
     c.status(404);
-    return c.render(<FourOhFour />);
+    const meta: SiteMeta = {
+      description: "Page does not exist."
+    };
+    return c.render(<FourOhFour />, { meta });
   }
 
   const post = await readPostMarkdown(__dirname + "/../../posts/" + postFile);
-  const meta = {
+  const meta: SiteMeta = {
     description: post.meta.description,
     tags: post.meta.tags,
     author: "Dave Smith-Hayes"