vlv search may result wrong result with lmdb

[progier389]

Issue Description
test_backup_and_restore_TestBackupAndRestoreWithReplica freeipa test is failing with 389ds main branch
(see freeipa-pr-ci2/freeipa#3346. )
screening from freeipa tests suspect that a vlv serach returns the wrong result (See https://pagure.io/freeipa/issue/9523)
( I am not surprising as the VLV handling code is quite complex with lmdb because lmdb does not support RECNO )

A clear and concise description of what the bug is.

Package Version and Platform:

• Platform: Fedora
• Package and version: 389-ds-base-3.0.0
• Browser: N/A

Steps to Reproduce
See https://pagure.io/freeipa/issue/9523
(Typically setup a ipa server and an ipa replica with CA then run ipa-healthcheck on the server)

Additional context
freeipa team may fix the issue as the VLV searches removal task progress, but we should fix it on 389ds too.

[progier389]

freeipa still get failure - there is a chicken and egg issue in my previous fix:
dbmdb_open_all_files to have the vlv initialized to open the vlv indexes
and vlv_init requires that be->be->instinfo->inst_id2index is set
Because of that we get:
[05/Mar/2024:11:15:02.114403616 +0100] - ERR - id2entry - Could not open id2entry err 0
[05/Mar/2024:11:15:02.121491509 +0100] - ERR - dn2entry_ext - The dn "ou=certificateRepository,ou=ca,o=ipaca" was in the entryrdn index, but it did not exist in id2entry of instance ipaca.
and everything is broken.
Can fix it by opening first id2entry then calling vlv_init then opening all the index files

[progier389]

Still an issue: covscan reported 2 potential NPE:
It is minor as minor and I am not even sure it is possible to trigger them without editing directly the dse.ldif
But I intend to fix them anyway to keep covscan report as small as possible

*** CID 1540758: Null pointer dereferences (NULL_RETURNS)
/ldap/servers/slapd/back-ldbm/vlv.c: 412 in vlv_list_filenames()
406 }
407
408 tmp_pb = slapi_search_internal(basedn, LDAP_SCOPE_SUBTREE, indexfilter, NULL, attrs, 0);
409 slapi_pblock_get(tmp_pb, SLAPI_PLUGIN_INTOP_SEARCH_ENTRIES, &entries);
410 for (size_t i = 0; entries && entries[i] != NULL; i++) {
411 const char *name = slapi_entry_attr_get_ref(entries[i], type_vlvName);

CID 1540758:  Null pointer dereferences  (NULL_RETURNS)
Dereferencing a pointer that might be "NULL" "name" when calling "vlvIndex_build_filename".

412 char *filename = vlvIndex_build_filename(name);
413 if (filename) {
414 charray_add(&names, filename);
415 }
416 }
417 slapi_free_search_results_internal(tmp_pb);

** CID 1540757: Null pointer dereferences (FORWARD_NULL)
/ldap/servers/slapd/back-ldbm/db-mdb/mdb_instance.c: 377 in dbmdb_open_all_files()

---

*** CID 1540757: Null pointer dereferences (FORWARD_NULL)
/ldap/servers/slapd/back-ldbm/db-mdb/mdb_instance.c: 377 in dbmdb_open_all_files()
371 char **vlv_list = NULL;
372 int ctxflags;
373 int rc = 0;
374 int i;
375
376 if (!ctx) {

CID 1540757:  Null pointer dereferences  (FORWARD_NULL)
Dereferencing null pointer "be".

377 struct ldbminfo *li = (struct ldbminfo )(be->be_database->plg_private);
378 ctx = MDB_CONFIG(li);
379 }
380 ctxflags = ctx->readonly ? MDB_RDONLY: MDB_CREATE;
381 if (does_vlv_need_init(inst)) {
382 / Vlv initialization is quite tricky as it require that