Followup to r1565531, Fix random failure of certs that don't have subjectAltNames.

* subversion/libsvn_ra_serf/util.c
  (ssl_server_cert): Initialize found_san_entry to FALSE.

Found by: julianf, philipm


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1568349 13f79535-47bb-0310-9956-ffa450edef68