Prior to this change, the `ResourceUrlEncodingFilter` would try to
lookup resources URLs as soon as the given URL would be longer than the
expected context+servlet prefix path. This can lead to
OutOfBoundsExceptions when the provided URL does not start with that
prefix and still has the required length.
This commit makes sure that all candidate URLs for resources lookup are
prefixed with the cached servlet and context path. This underlines the
fact that the `ResourceUrlEncodingFilter` does not support relative URLs
for now and delegates to the native servlet implementation in that case.
Issue: SPR-13861
2f6d86b7aa