s4 dsdb: fix use after free in samldb_rename_search_base_callback

s4 dsdb: fix use after free in samldb_rename_search_base_callback

Fix use after free detected by AddressSanitizer

AddressSanitizer: heap-use-after-free on address 0x60f0002b2738
                  at pc 0x7f89b1a213b5 bp 0x7ffce9528810 sp 0x7ffce9528800
                  READ of size 8 at 0x60f0002b2738 thread T0
    #0 0x7f89b1a213b4 in samldb_rename_search_base_callback
        ../../source4/dsdb/samdb/ldb_modules/samldb.c:4203
    #1 0x7f89d3a0db4a in ldb_module_send_entry
        ../../lib/ldb/common/ldb_modules.c:793
    #2 0x7f89b6f27356 in es_callback
        ../../source4/dsdb/samdb/ldb_modules/encrypted_secrets.c:1418

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13942

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>