Allow the Web IDE to open empty merge requests

Closes #48166

app/assets/javascripts/ide/ide_router.js

@@ -117,7 +117,7 @@ router.beforeEach((to, from, next) => {
               mergeRequestId: to.params.mrid,
             })
             .then(mr => {
-              store.dispatch('updateActivityBarView', activityBarViews.review);
+              store.dispatch('setCurrentBranchId', mr.source_branch);
 
               store.dispatch('getBranchData', {
                 projectId: fullProjectId,
@@ -144,6 +144,10 @@ router.beforeEach((to, from, next) => {
               }),
             )
             .then(mrChanges => {
+              if (mrChanges.changes.length) {
+                store.dispatch('updateActivityBarView', activityBarViews.review);
+              }
+
               mrChanges.changes.forEach((change, ind) => {
                 const changeTreeEntry = store.state.entries[change.new_path];
 

changelogs/unreleased/ide-open-empty-merge-request.yml

+---
+title: Fix empty merge requests not opening in the Web IDE
+merge_request:
+author:
+type: fixed