Fix a bug with dbm rewrite maps which caused the wrong value to

be used when the key was not found in the dbm.

apr_dbm_fetch() returns APR_SUCCESS as long as there was no I/O
error.  mod_rewrite needed to look further to see if the key
was actually found.

PR 13204


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97106 13f79535-47bb-0310-9956-ffa450edef68