auth:credentials: Check if password_obtained > obtained

auth:credentials: Check if password_obtained > obtained

Fixes reading the password from STDIN or environment vars if it was already
given in the command line:

$ export PASSWD_FD=0
$ ./bin/net offlinejoin composeodj <...> --password=FOO
<Waiting to read password from STDIN>

Signed-off-by: Samuel Cabrero <scabrero@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Mon Sep 11 03:36:28 UTC 2023 on atb-devel-224