Fix `ResourceUrlEncodingFilter` conditions which were inadvertently
changed in commits 64f04fce and 6cc272ec and would back off if any
`FilterRegistrationBean` was found.

The updated conditions restores the behavior of Spring Boot 2.0.5 and
allows users to directly register their own `ResourceUrlEncodingFilter`
beans (as long as they don't use a `FilterRegistrationBean`).

Fixes gh-14897