fix Invalid read of size 8

fix Invalid read of size 8

running rpc.dsgetinfo.DsGetReplicaInfo results in the following valgrind
trace

==14966== Invalid read of size 8
==14966==    at 0x88B2D5D: dcerpc_binding_handle_call (binding_handle.c:538)
==14966==    by 0x978F33B: dcerpc_drsuapi_DsUnbind_r (ndr_drsuapi_c.c:319)
==14966==    by 0x2E9F19: torture_dsgetinfo_tcase_teardown (dsgetinfo.c:431)
==14966==    by 0x95536EF: internal_torture_run_test (torture.c:452)
==14966==    by 0x9553A4B: torture_run_test_restricted (torture.c:542)
==14966==    by 0x260074: run_matching (smbtorture.c:110)
==14966==    by 0x25FF36: run_matching (smbtorture.c:95)
==14966==    by 0x260195: torture_run_named_tests (smbtorture.c:143)
==14966==    by 0x261E14: main (smbtorture.c:665)
==14966==  Address 0x28 is not stack'd, malloc'd or (recently) free'd
==14966==

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Mon Apr 25 14:01:33 CEST 2016 on sn-devel-144