Fixed bug introduced by changeover of security descriptor code from

Fixed bug introduced by changeover of security descriptor code from
malloc() to talloc().  Previously, creating an ACL containing zero ACEs
would return a non-NULL pointer to zero bytes of memory.  The talloc() code
would return a NULL pointer making the ACL a NULL ACL instead of an empty
one.  The difference is a NULL ACL allows all access and an empty ACL
denies all access.

We solve this by calling talloc(ctx, sizeof(SEC_ACE) * num_aces + 1).
Heh.
(This used to be commit 89eaaafe7d266788609fab6951fd912c441b3a26)