scroll: return 204 instead of 404 for empty scroll responses

404 means the resource doesn't exist; 204 (No Content) correctly signals
that pagination reached the end. The JS fetch handler now checks for any
non-2xx status instead of only 404, so it stops scrolling on 204 too.

public/js/infiniteScroll.js

@@ -40,7 +40,7 @@ window.onload = function () {
             url.searchParams.append("scroll", "true");
 
             fetch(url.toString()).then(function (response) {
-                if (response.status === 404) throw "error";
+                if (response.status > 299) throw "error";
 
                 return response.text();
             }).then(function (html) {

src/routes/status.rs

@@ -168,7 +168,7 @@ async fn status(
          // Check this first — paginated responses don't include the main tweet.
          if is_scroll {
             if conversation.replies.content.is_empty() {
-               return Ok(StatusCode::NOT_FOUND.into_response());
+               return Ok(StatusCode::NO_CONTENT.into_response());
             }
             let content = render_reply_chains(
                &conversation.replies.content,