source4/librpc: Add NULL check in dcerpc_secondary_auth_connection()

source4/librpc: Add NULL check in dcerpc_secondary_auth_connection()

When dcerpc_secondary_auth_connection_send() fails, it returns NULL.
The NULL pointer is passed to dcerpc_secondary_auth_connection_recv()
which dereferences it without checking, causing a NULL pointer
dereference.

Add NULL check before calling the recv function and return
NT_STATUS_NO_MEMORY.

Signed-off-by: Anoop C S <anoopcs@samba.org>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Thu May 21 03:24:09 UTC 2026 on atb-devel-224