Bug 1193243

This bug is created as a clone of upstream ticket:
https://fedorahosted.org/389/ticket/47659

==26183==
==26183== Invalid read of size 8
==26183==    at 0xFF0E29C: ldbm_usn_init (ldbm_usn.c:83)
==26183==    by 0xFF20786: ldbm_back_start (start.c:300)
==26183==    by 0x4CC34E3: plugin_call_func (plugin.c:1474)
==26183==    by 0x4CC33D0: plugin_call_one (plugin.c:1442)
==26183==    by 0x4CC2BE1: plugin_dependency_startall (plugin.c:1214)
==26183==    by 0x4CC3302: plugin_startall (plugin.c:1404)
==26183==    by 0x12F3CA: main (main.c:1187)
==26183==  Address 0x80 is not stack'd, malloc'd or (recently) free'd
==26183==
==26183==
==26183== Process terminating with default action of signal 11 (SIGSEGV)
==26183==  Access not within mapped region at address 0x80
==26183==    at 0xFF0E29C: ldbm_usn_init (ldbm_usn.c:83)
==26183==    by 0xFF20786: ldbm_back_start (start.c:300)
==26183==    by 0x4CC34E3: plugin_call_func (plugin.c:1474)
==26183==    by 0x4CC33D0: plugin_call_one (plugin.c:1442)
==26183==    by 0x4CC2BE1: plugin_dependency_startall (plugin.c:1214)
==26183==    by 0x4CC3302: plugin_startall (plugin.c:1404)
==26183==    by 0x12F3CA: main (main.c:1187)
==26183==  If you believe this happened as a result of a stack
==26183==  overflow in your program's main thread (unlikely but
==26183==  possible), you can try to increase the size of the
==26183==  main thread stack using the --main-stacksize= flag.
==26183==  The main thread stack size used in this run was 8388608.
==26183==

 62 void
 63 ldbm_usn_init(struct ldbminfo  *li)
    ...
 79     /* Search each namingContext in turn */
 80     for ( sdn = slapi_get_first_suffix( &node, 0 ); sdn != NULL;
 81           sdn = slapi_get_next_suffix_ext( &node, 0 )) {
 82         be = slapi_mapping_tree_find_backend_for_sdn(sdn);
 83         slapi_log_error(SLAPI_LOG_BACKLDBM, "ldbm_usn_init",
 84                     "backend: %s%s\n", be->be_name, isglobal?" (global mode)":""); <== crashed here; slapi_mapping_tree_find_backend_for_sdn returned 0x80?