mod_slotmem_shm: Fix slots/SHM files names on restart for systems that

can't create new (clear) slots while previous children gracefully stopping
still use the old ones (e.g. Windows, OS2). PR 58024.

Submitted by: ylavic
Reviewed by: jim, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1705499 13f79535-47bb-0310-9956-ffa450edef68