Coverity defects
12811: Unused pointer value
preop_modrdn (plugins/uiduniq/uid.c)
Removed unused variable "dn".
12812: Unused pointer value
ldbm_back_next_search_entry_ext (slapd/back-ldbm/ldbm_search.c)
Removed unused variable "base".
12813: Uninitialized pointer read
string_values2keys (plugins/syntaxes/string.c)
Commit f6b74ad18a52720c4558d4a46cbb2eeb21109033 missed to set
an value bvp for the newly added case ((syntax & SYNTAX_DN) &&
(value_flags & SLAPI_ATTR_FLAG_NORMALIZED_CES)), which caused
the uninitialized pointer read. This patch sets bvp for all
3 cases.