mod_authz_svn: Avoid duplicate calls to ap_some_auth_required().

The answer from ap_some_auth_required() isn't going to change between
these calls. 

* subversion/mod_authz_svn/mod_authz_svn.c
  (access_checker): Don't call ap_some_auth_required() twice.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1511476 13f79535-47bb-0310-9956-ffa450edef68