Fixed image discussions not showing on the changes tab

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/225922

app/assets/javascripts/diffs/store/mutations.js

@@ -248,7 +248,7 @@ export default {
           });
         }
 
-        if (!file.parallel_diff_lines || !file.highlighted_diff_lines) {
+        if (!file.parallel_diff_lines.length || !file.highlighted_diff_lines.length) {
           const newDiscussions = (file.discussions || [])
             .filter(d => d.id !== discussion.id)
             .concat(discussion);

changelogs/unreleased/ph-225922-fixedImageDiscussionsNotShowingOnChangesTab.yml

+---
+title: Fixed image comments not showing on the changes tab
+merge_request:
+author:
+type: fixed

spec/frontend/diffs/store/mutations_spec.js

@@ -645,6 +645,36 @@ describe('DiffsStoreMutations', () => {
       expect(state.diffFiles[0].highlighted_diff_lines[0].discussions).toHaveLength(1);
       expect(state.diffFiles[0].highlighted_diff_lines[0].discussions[0].id).toBe(1);
     });
+
+    it('should add discussion to file', () => {
+      const state = {
+        latestDiff: true,
+        diffFiles: [
+          {
+            file_hash: 'ABC',
+            discussions: [],
+            parallel_diff_lines: [],
+            highlighted_diff_lines: [],
+          },
+        ],
+      };
+      const discussion = {
+        id: 1,
+        line_code: 'ABC_1',
+        diff_discussion: true,
+        resolvable: true,
+        diff_file: {
+          file_hash: state.diffFiles[0].file_hash,
+        },
+      };
+
+      mutations[types.SET_LINE_DISCUSSIONS_FOR_FILE](state, {
+        discussion,
+        diffPositionByLineCode: null,
+      });
+
+      expect(state.diffFiles[0].discussions.length).toEqual(1);
+    });
   });
 
   describe('REMOVE_LINE_DISCUSSIONS', () => {