Fix currentDiffFileId being set incorrectly

This can happen when a note on a diff file that no longer exists
is linked to.

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

@@ -743,14 +743,14 @@ export function moveToNeighboringCommit({ dispatch, state }, { direction }) {
   }
 }
 
-export const setCurrentDiffFileIdFromNote = ({ commit, rootGetters }, noteId) => {
+export const setCurrentDiffFileIdFromNote = ({ commit, state, rootGetters }, noteId) => {
   const note = rootGetters.notesById[noteId];
 
   if (!note) return;
 
   const fileHash = rootGetters.getDiscussion(note.discussion_id).diff_file?.file_hash;
 
-  if (fileHash) {
+  if (fileHash && state.diffFiles.some(f => f.file_hash === fileHash)) {
     commit(types.UPDATE_CURRENT_DIFF_FILE_ID, fileHash);
   }
 };

spec/frontend/diffs/store/actions_spec.js

@@ -1594,24 +1594,39 @@ describe('DiffsStoreActions', () => {
   describe('setCurrentDiffFileIdFromNote', () => {
     it('commits UPDATE_CURRENT_DIFF_FILE_ID', () => {
       const commit = jest.fn();
+      const state = { diffFiles: [{ file_hash: '123' }] };
       const rootGetters = {
         getDiscussion: () => ({ diff_file: { file_hash: '123' } }),
         notesById: { '1': { discussion_id: '2' } },
       };
 
-      setCurrentDiffFileIdFromNote({ commit, rootGetters }, '1');
+      setCurrentDiffFileIdFromNote({ commit, state, rootGetters }, '1');
 
       expect(commit).toHaveBeenCalledWith(types.UPDATE_CURRENT_DIFF_FILE_ID, '123');
     });
 
     it('does not commit UPDATE_CURRENT_DIFF_FILE_ID when discussion has no diff_file', () => {
       const commit = jest.fn();
+      const state = { diffFiles: [{ file_hash: '123' }] };
       const rootGetters = {
         getDiscussion: () => ({ id: '1' }),
         notesById: { '1': { discussion_id: '2' } },
       };
 
-      setCurrentDiffFileIdFromNote({ commit, rootGetters }, '1');
+      setCurrentDiffFileIdFromNote({ commit, state, rootGetters }, '1');
+
+      expect(commit).not.toHaveBeenCalled();
+    });
+
+    it('does not commit UPDATE_CURRENT_DIFF_FILE_ID when diff file does not exist', () => {
+      const commit = jest.fn();
+      const state = { diffFiles: [{ file_hash: '123' }] };
+      const rootGetters = {
+        getDiscussion: () => ({ diff_file: { file_hash: '124' } }),
+        notesById: { '1': { discussion_id: '2' } },
+      };
+
+      setCurrentDiffFileIdFromNote({ commit, state, rootGetters }, '1');
 
       expect(commit).not.toHaveBeenCalled();
     });