mod_slotmem_shm: follow up tp r1822509.

Complete layout of SHM and persited file (ascii art).
Simplify an "if" condition, no functional change.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1823416 13f79535-47bb-0310-9956-ffa450edef68