[Snippets] Add error handling to rewrite-site-links.mdx (#23075)

Author: pedrosousa

src/content/docs/rules/snippets/examples/rewrite-site-links.mdx

@@ -40,7 +40,13 @@ export default {
             .on("img", new AttributeRewriter("src"));
 
         const res = await fetch(request);
+        if (!res.headers.has("Content-Type")) {
+            return res;
+        }
         const contentType = res.headers.get("Content-Type");
+        if (typeof contentType !== "string") {
+            return res;
+        }
 
         // If the response is HTML, it can be transformed with
         // HTMLRewriter -- otherwise, it should pass through
@@ -51,4 +57,4 @@ export default {
         }
     },
 };
-```
+```