If the SiteSetting `allowed_onebox_iframes` contains a value of `*`, it will use the values of `all_iframe_origins` during the Oneboxing process. If `all_iframe_origins` itself contains a value of `*`, `origins_to_regexes` will try to return a "catch-all" regex.
Other code assumes `origins_to_regexes`will return an array, so this change ensures the `*` case will return an array containing only the catch-all regex.
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