Address console error on settings page

[bjackson27]

Looks like the tag searching code is search a null value. Probably not a functionality breaking bug, however worth fixing.

The error occurs here:

This is a regression and likely broke when we changed how/when the tag detecting iframe is loaded.

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Changelog entry

• Fix console error on settings page while checking for existing analytics tag

Acceptance criteria

• No console errors should show on the settings page.