Fix public timeline page not paginating correctly (#10245)

app/javascript/mastodon/features/standalone/public_timeline/index.js

@@ -60,10 +60,14 @@ class PublicTimeline extends React.PureComponent {
     }
   }
 
-  handleLoadMore = maxId => {
-    const { dispatch, local } = this.props;
+  handleLoadMore = () => {
+    const { dispatch, statusIds, local } = this.props;
+    const maxId = statusIds.last();
+
+    if (maxId) {
       dispatch(local ? expandCommunityTimeline({ maxId }) : expandPublicTimeline({ maxId }));
     }
+  }
 
   setRef = c => {
     this.masonry = c;