Should switch to one of the available options if given option is not available to the current document

[hikalkan]

Visit this URL: https://docs.abp.io/en/abp/latest/Getting-Started?UI=React&DB=EF&Tiered=No

We have no React UI, seems it fallbacks to MVC, which is a true behavior. However, the fact is not that;

1. Inside the document, I see **** as the UI Framework.
2. UI variable is still React, so the document is not correctly rendered (because of if conditions).

So, it should gracefully fallback to the first option and also update the cookie.