Don't try to show timezone or iframe warning if not present

[jorg-vr]

This pull request fixes #5572

I also applied the same fix for check Iframe, but I am open for discussion on that one, as we might want to get notified should that warning not be present when desired.

Closes #5572.

[bmesuere]

(I don't think the second ?. on each line is needed but no harm down with including it.)

Did you see errors for checkIframe on Sentry?

[jorg-vr]

We haven't yet encountered the iFrameIssue on sentry. It was just right below in the code, so my I fell upon it

And yes the second ?. is required

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ TypeError: null is not an object (evaluating 'document.querySelector("#time-zone-warning").classList') checkTimeZone(app/assets/javascripts/utilities) View Issue

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