ndr: short-circuit ace coda if no bytes left

ndr: short-circuit ace coda if no bytes left

The overwhelmingly common case is that there are no bytes left, and
regardless of the ACE type we want to store an empty blob.

We know the blob will be empty if there are no bytes, so we don't need
to allocate a sub-ndr and tokens list and so forth.

This can save almost half the time of a security descriptor pull.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15574
(cherry picked from commit ac0c8ee01ea624e9c486251da2132710c2a43ddc)