Fix fatal strangler error when using `theme_option_admin` pref

• Fix fatal strangler error when using theme_option_admin pref

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• [FIX] theme: Fix fatal strangler error when using theme_option_admin pref - this and theme_admin don't have a site_ prefixed version as they're not overridable by the user (i think).

Better refactoring and modernisation of all this needed (one day...)

See merge request !4919 (merged)

(cherry picked from commit ca0ab61a)

c8181e10 [FIX] theme: Fix fatal stragler error when using theme_option_admin pref -...

Co-authored-by: Jonny Bradley jmail@nospaces.net