s3:passdb: Do not leak memory if memcache add fails

s3:passdb: Do not leak memory if memcache add fails

Indirect leak of 496 byte(s) in 1 object(s) allocated from:
    #0 0x7ffb062dc03f in malloc (/lib64/libasan.so.8+0xdc03f) (BuildId: 3e1694ad218c99a8b1b69231666a27df63cf19d0)
    #1 0x7ffb06025b3e in __talloc_with_prefix ../../lib/talloc/talloc.c:783
    #2 0x7ffb06027512 in __talloc ../../lib/talloc/talloc.c:825
    #3 0x7ffb06027512 in _talloc_named_const ../../lib/talloc/talloc.c:982
    #4 0x7ffb06027512 in _talloc_zero ../../lib/talloc/talloc.c:2421
    #5 0x7ffb05a0332c in samu_new ../../source3/passdb/passdb.c:63
    #6 0x7ffb05a2031f in pdb_getsampwnam ../../source3/passdb/pdb_interface.c:351
    #7 0x7ffb05a0540b in local_password_change ../../source3/passdb/passdb.c:752
    #8 0x56291ddd4b8b in password_change ../../source3/utils/smbpasswd.c:273
    #9 0x56291ddd5b59 in process_root ../../source3/utils/smbpasswd.c:478
    #10 0x56291ddd5b59 in main ../../source3/utils/smbpasswd.c:661
    #11 0x7ffb024281af in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>