No results fetched on search if scope(only_in_search) is disabled in settings page by user

Since scope with only_in_search property enabled is mainly used to search stuff and display results on search.
It causes searching feature won't work if user disable the scope in settings page.

I think the optimal way for this is hide only_in_search scope name in settings page.
By far we can't find a way to do so based on current scope framework. Aggregator will check its all children scopes and display their name in settings page.