mod_cache: Fix a regression in 2.4.25 for the forward proxy case by

computing and using the same entity key according to when the cache
checks, loads and saves the request.  PR 60577.
 


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1783842 13f79535-47bb-0310-9956-ffa450edef68