fix(client): ensure presetEnv is loaded (#39431)

Prior to this, if a user first loaded a React challenge and then
navigated to a JS challenge, they would see
TypeError: Cannot read property 'presets' of undefined
in the console and be unable to run tests or evaluate code until they
reloaded the page.

client/src/templates/Challenges/rechallenge/transformers.js

@@ -59,8 +59,9 @@ async function loadBabel() {
 }
 
 async function loadPresetEnv() {
-  if (presetEnv) return;
+  if (babelOptionsJSBase && babelOptionsJSBase.presets) return;
   /* eslint-disable no-inline-comments */
+  if (!presetEnv)
     presetEnv = await import(
       /* webpackChunkName: "@babel/preset-env" */ '@babel/preset-env'
     );