Fix `Undefined array key "enabledThemes"` on layout.user.php
Fix `Undefined array key "enabledThemes"` on layout.user.php

Signed-off-by: John Molakvoæ <0835dbafb601d1e4088d26d0286d7121ba48453b@protonmail.com>

nextcloud/server,nextcloud/server,nextcloud/server,nextcloud/server