apr_file_write_full() simplification (like r1542413 and r1542416)

hopefully I sidestepped the surprising conflation of OK/APR_SUCCESS
in this code


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1542493 13f79535-47bb-0310-9956-ffa450edef68