Fixed failing Jest specs

This was caused by a Vuex store getting setup when it didn't
need to be setup.

app/assets/javascripts/code_navigation/index.js

 import Vue from 'vue';
 import Vuex from 'vuex';
-import store from './store';
+import createStore from './store';
 import App from './components/app.vue';
 
-Vue.use(Vuex);
-
 export default initialData => {
   const el = document.getElementById('js-code-navigation');
 
+  if (!el) return null;
+
+  Vue.use(Vuex);
+
+  const store = createStore();
+
   store.dispatch('setInitialData', initialData);
 
   return new Vue({

app/assets/javascripts/code_navigation/store/index.js

@@ -3,8 +3,9 @@ import createState from './state';
 import actions from './actions';
 import mutations from './mutations';
 
-export default new Vuex.Store({
-  actions,
-  mutations,
-  state: createState(),
-});
+export default () =>
+  new Vuex.Store({
+    actions,
+    mutations,
+    state: createState(),
+  });

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

@@ -103,18 +103,20 @@ export const fetchDiffFilesBatch = ({ commit, state, dispatch }) => {
             commit(types.VIEW_DIFF_FILE, state.diffFiles[0].file_hash);
           }
 
-          // eslint-disable-next-line promise/catch-or-return,promise/no-nesting
-          import('~/code_navigation').then(m =>
-            m.default({
-              blobs: state.diffFiles
-                .filter(f => f.code_navigation_path)
-                .map(f => ({
-                  path: f.new_path,
-                  codeNavigationPath: f.code_navigation_path,
-                })),
-              definitionPathPrefix: state.definitionPathPrefix,
-            }),
-          );
+          if (state.diffFiles?.length) {
+            // eslint-disable-next-line promise/catch-or-return,promise/no-nesting
+            import('~/code_navigation').then(m =>
+              m.default({
+                blobs: state.diffFiles
+                  .filter(f => f.code_navigation_path)
+                  .map(f => ({
+                    path: f.new_path,
+                    codeNavigationPath: f.code_navigation_path,
+                  })),
+                definitionPathPrefix: state.definitionPathPrefix,
+              }),
+            );
+          }
         }
 
         return pagination.next_page;