CVE-2019-3824 ldb: wildcard_match end of data check

CVE-2019-3824 ldb: wildcard_match end of data check

ldb_handler_copy and ldb_val_dup over allocate by one and add a trailing '\0'
to the data, to make them safe to use the C string functions on.

However testing for the trailing '\0' is not the correct way to test for
the end of a value, the length should be checked instead.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13773

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
(cherry picked from commit 42f0f57eb819ce6b68a8c5b3b53123b83ec917e3)