mod_dav: When a PROPPATCH attempts to remove a non-existent dead

property on a resource for which there is no dead property in the same
namespace httpd segfaults. PR 52559
Submitted by Diego Santa Cruz <diego.santaCruz spinetix.com>
Tested by William Lewis <wiml omnigroup com>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1476642 13f79535-47bb-0310-9956-ffa450edef68