Fix a nasty segfault in mmap_bucket_setaside() caused by passing

an incompatible pointer type to mmap_bucket_destroy(void*).

PR:            16533
Submitted by:  Gerard Eviston <geviston@bigpond.net.au>
Reviewed by:   Cliff Woolley


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@98538 13f79535-47bb-0310-9956-ffa450edef68