ra_serf: Improve code readability in the certificate validation code.

* subversion/libsvn_ra_serf/util.c
  (ssl_server_cert): Remove a boolean and use an else block instead.

Suggested by: ivan


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1615272 13f79535-47bb-0310-9956-ffa450edef68