Merge updateTabRank into calling function

The code is only used in one place with the same branching. Merging it
seems more readable.

No functional changes intended.

Author: Kevinjil

webapp/public/js/domjudge.js

@@ -1339,8 +1339,9 @@ function initDiffEditor(editorId) {
 
     const download = wrapper.find(".download")[0];
     const edit = wrapper.find(".edit")[0];
-    const updateTabRank = (rank) => {
-        if (rank !== undefined) {
+    wrapper.find(".nav").on('show.bs.tab', (e) => {
+        if (e.target.dataset.rank.length > 0) {
+            const rank = parseInt(e.target.dataset.rank);
             let url = new URL(download.href);
             url.searchParams.set("fetch", rank);
             enableButton(download, url);
@@ -1352,14 +1353,6 @@ function initDiffEditor(editorId) {
             disableButton(download);
             disableButton(edit);
         }
-    };
-    wrapper.find(".nav").on('show.bs.tab', (e) => {
-        if (e.target.dataset.rank.length > 0) {
-            const rank = parseInt(e.target.dataset.rank);
-            updateTabRank(rank);
-        } else {
-            updateTabRank(undefined);
-        }
     })
 
     const diffTitle = document.getElementById(`${editorId}-title-diff`);