mod_dav: Do not fail PROPPATCH when prop namespace is not known. PR 52559

trunk patch: http://svn.apache.org/r1476644
Submitted by: Diego Santa Cruz <diego.santaCruz spinetix.com>
Reviewed by: minfrin, jim, jorton


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1486459 13f79535-47bb-0310-9956-ffa450edef68