Abort DAG app init if selector doesn't exist

app/assets/javascripts/pipelines/pipeline_details_bundle.js

@@ -147,6 +147,9 @@ const createTestDetails = detailsEndpoint => {
 
 const createDagApp = () => {
   const el = document.querySelector('#js-pipeline-dag-vue');
+  if (!el) {
+    return;
+  }
   const graphUrl = el.dataset?.pipelineDataPath;
   // eslint-disable-next-line no-new
   new Vue({

changelogs/unreleased/219022-fix-pipelines-apps-not-loading.yml

+---
+title: Fix a bug where some Vue apps would be unable to load when DAG tab is disabled
+merge_request: 32966
+author:
+type: fixed