Fix bug where analytics tries to init in tests which don't import it

[AshGDS]

Hi @andysellick,

Would you be able to approve this if all is OK?

Thanks 👍

What

We want the analytics to load in if it hasn't been already, which is why we check for undefined values, and load in analytics if the values are undefined.

However, our tests do not import load-analytics.js by default, so having a nested check like window.GOVUK.analyticsGa4.vars resulted in an error in our tests, as window.GOVUK.analyticsGa4 didn't exist, so we couldn't run a check on window.GOVUK.analyticsGa4.vars without the JS crashing.

Therefore I have added extra if statements which ensure this code only runs when we can guarantee that load-analytics.js has been imported.

I've checked this against the Jasmine tests in frontend, finder-frontend, and government-frontend and they're now passing.

Why

Without this, tests across our applications to fail, because the DOMContentLoaded code was running on tests which did not have load-analytics.js loaded into the DOM (which is imported only when _layout_for_public is rendered. So window.GOVUK.analyticsGa4 did not exist and then the window.GOVUK.analyticsGa4.vars check would crash.

Visual Changes

None.

[andysellick]

🚀