mod_proxy: Follow up to r1892814.

* modules/proxy/proxy_util.c(fix_uds_filename):
  Sanity checks on the configured UDS path, fail with 500 if invalid since
  continuing through proxy processing wouldn't work as expected.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1892986 13f79535-47bb-0310-9956-ffa450edef68
