v8.0.7 minor adjustments

Minor adjustments:

1. No need to include sitemap.xml as a suspicious path in the minum.config, it is a path
   most search engines will try on a site, it is not an attack.
2. If the developer makes a mistake and returns a null instead of a valid IResponse interface
   from a web handler endpoint, we fail faster, and with a clearer message, whereas before
   the null response would rattle around through some methods before causing an exception with
   an unclear error message and in an unexpected part of the code.